It is thought that  ultraviolet (UV) radiation  induces mutations in the keratinocytes of the epidermis, promoting the survival and proliferation of these atypical cells. Both  UV-A  and  UV-B  radiation have been implicated as causes of AKs.  UV-A radiation (wavelength 320–400 nm) reaches more deeply into the skin and can lead to the generation of  reactive oxygen species , which in turn can damage cell membranes, signaling proteins, and nucleic acids.   UV-B  radiation (wavelength 290–320 nm) causes  thymidine   dimer  formation in DNA and RNA, leading to significant cellular mutations. [ 30 ]   In particular, mutations in the p53 tumor suppressor gene have been found in 30–50% of AK lesion skin samples. [ 26 ] [ 28 ]


UV radiation has also been shown to cause elevated inflammatory markers such as  arachidonic acid , as well as other molecules associated with inflammation. [ 27 ]   Eventually, over time these changes lead to the formation of AKs.  Several predictors for increased AK risk from UV radiation have been identified:


Melanin  is a pigment in the epidermis that functions to protect keratinocytes from the damage caused by UV radiation; it is found in higher concentrations in the epidermis of darker-skinned individuals, affording them protection against the development of AKs.


Fair-skinned individuals have a significantly increased risk of developing AKs when compared to olive-skinned individuals ( odds ratios  of 14.1 and 6.5, respectively), [ 33 ]  and AKs are uncommon in dark-skinned people of African descent. [ 31 ]  Other phenotypic features seen in fair-skinned individuals that are associated with an increased propensity to develop AKs include: [ 31 ]


Physicians usually diagnose actinic keratosis by doing a thorough physical examination, through a combination of visual observation and touch. However a  biopsy  may be necessary when the keratosis is large in diameter, thick, or bleeding, in order to make sure that the lesion is not a  skin cancer . Actinic keratosis may progress to invasive  squamous cell carcinoma  (SCC) but both diseases can present similarly upon physical exam and can be difficult to distinguish clinically. [ 6 ]


Histological  examination of the lesion from a  biopsy  or excision may be necessary to definitively distinguish AK from  in situ  or invasive  SCC . [ 6 ]  In addition to SCCs, AKs can be mistaken for other  cutaneous  lesions including  seborrheic keratoses ,  basal cell carcinoma ,  lichenoid keratosis ,  porokeratosis ,  viral warts ,  erosive pustular dermatosis of the scalp ,  pemphigus foliaceus , inflammatory dermatoses like  psoriasis , or  melanoma . [ 38 ]


A lesion  biopsy  is performed if the diagnosis remains uncertain after a clinical physical exam, or if there is suspicion that the AK might have progressed to squamous cell carcinoma. The most common tissue sampling techniques include shave or punch biopsy. When only a portion of the lesion can be removed due to its size or location, the biopsy should sample tissue from the thickest area of the lesion, as SCCs are most likely to be detected in that area.


If a  shave biopsy  is performed, it should extend through to the level of the  dermis  in order to provide sufficient tissue for diagnosis; ideally, it would extend to the mid-reticular dermis.  Punch biopsy  usually extends to the  subcutaneous fat  when the entire length of the punch blade is utilized.


On histologic examination, actinic keratoses usually show a collection of atypical keratinocytes with hyperpigmented or pleomorphic nuclei, extending to the  basal layer  of the  epidermis . A "flag sign" is often described, referring to alternating areas of  orthokeratosis  and  parakeratosis .  Epidermal thickening  and surrounding areas of  sun-damaged skin  are often seen. [ 39 ]  The normal ordered maturation of the  keratinocytes  is disordered to varying degrees: there may be widening of the intracellular spaces, cytologic atypia such as abnormally large nuclei, and a mild  chronic inflammatory  infiltrate. [ 40 ]


Specific findings depend on the clinical variant and particular lesion characteristics. The seven major histopathologic variants are all characterized by atypical keratinocytic proliferation beginning in the basal layer and confined to the epidermis; they include: [ 39 ]


Dermoscopy  is a noninvasive technique utilizing a handheld magnifying device coupled with a transilluminating lift. It is often used in the evaluation of cutaneous lesions but lacks the definitive diagnostic ability of biopsy-based tissue diagnosis. Histopathologic exam remains the gold standard.


Polarized contact dermoscopy of AKs occasionally reveals a "rosette sign," described as four white points arranged in a clover pattern, often localized to within a follicular opening. [ 41 ]  It is hypothesized that the "rosette sign" corresponds histologically to the changes of orthokeratosis and parakeratosis known as the "flag sign." [ 41 ]


Ultraviolet radiation is believed to contribute to the development of actinic keratoses by inducing mutations in epidermal keratinocytes, leading to proliferation of atypical cells. [ 44 ]  Therefore, preventive measures for AKs are targeted at limiting exposure to solar radiation, including:


Recent research implicating human papillomavirus (HPV) in the development of AKs suggests that HPV prevention might in turn help prevent development of AKs, as UV-induced mutations and oncogenic transformation are likely facilitated in cases of active HPV infection. [ 29 ]   A key component of HPV prevention includes  vaccination , and the CDC currently recommends routine vaccination in all children at age 11 or 12. [ 47 ]


There are some data that in individuals with a history of non-melanoma skin cancer, a low-fat diet can serve as a preventative measure against future actinic keratoses. [ 38 ]


There are a variety of treatment options for AK depending on the patient and the clinical characteristics of the lesion.  AKs show a wide range of features, which guide decision-making in choosing treatment. As there are multiple effective treatments, patient preference and lifestyle are also factors that physicians consider when determining the management plan for actinic keratosis. [ 48 ]  Regular follow-up is advisable after any treatment to make sure no new lesions have developed and that old ones are not progressing. Adding topical treatment after a procedure may improve outcomes. [ 49 ]


Topical medications are often recommended for areas where multiple or ill-defined AKs are present, as the medication can easily be used to treat a relatively large area. [ 48 ]


Topical  fluorouracil  (5-FU) destroys AKs by blocking  methylation  of  thymidylate synthetase , thereby interrupting DNA and RNA synthesis. [ 50 ]  This in turn prevents the proliferation of dysplastic cells in AK. Topical 5-FU is the most utilized treatment for AK, and often results in effective removal of the lesion. [ 51 ]  Overall, there is a 50% efficacy rate resulting in 100% clearance of AKs treated with topical 5-FU. [ 52 ] [ 53 ]  5-FU may be up to 90% effective in treating non-hyperkeratotic lesions. [ 54 ]  While topical 5-FU is a widely used and cost-effective treatment for AKs and is generally well tolerated, its potential side-effects can include: pain, crusting, redness, and local swelling. [ 55 ]  These adverse effects can be mitigated or minimized by reducing the frequency of application or taking breaks between uses. [ 55 ]  The most commonly used application regimen consists of applying a layer of topical cream to the lesion twice a day after washing; duration of treatment is typically 2–4 weeks to thinner skin like the cheeks and up to 8 weeks for the arms; treatment of up to 8 weeks has demonstrated a higher cure rate. [ 56 ] [ 57 ]


Imiquimod  is a topical immune-enhancing agent licensed for the treatment of genital warts. [ 25 ]  Imiquimod stimulates the  immune system  through the release and up-regulation of  cytokines . [ 56 ]  Treatment with Imiquimod cream applied 2–3 times per week for 12 to 16 weeks was found to result in complete resolution of AKs in 50% of people, compared to 5% of controls. [ 58 ]  The Imiquimod 3.75% cream has been validated in a treatment regimen consisting of daily application to entire face and scalp for two 2-week treatment cycles, with a complete clearance rate of 36%. [ 59 ]


While the clearance rate observed with the Imiquimod 3.75% cream was lower than that observed with the 5% cream (36 and 50 percent, respectively), there are lower reported rates of adverse reactions with the 3.75% cream: 19% of individuals using Imiquimod 3.75% cream reported adverse reactions including local erythema, scabbing, and flaking at the application site, while nearly a third of individuals using the 5% cream reported the same types of reactions with Imiquimod treatment. [ 58 ] [ 59 ]  However, it is ultimately difficult to compare the efficacy of the different strength creams directly, as current study data varies in methodology (e.g. duration and frequency of treatment, and amount of skin surface area covered).


Ingenol mebutate  is a newer treatment for AK used in Europe and the United States. It works in two ways, first by disrupting cell membranes and mitochondria resulting cell death, and then by inducing antibody-dependent cellular cytotoxicity to eliminate remaining tumor cells. [ 60 ]  A 3-day treatment course with the 0.015% gel is recommended for the scalp and face, while a 2-day treatment course with the 0.05% gel is recommended for the trunk and extremities. [ 61 ]  Treatment with the 0.015% gel was found to completely clear 57% of AK, while the 0.05% gel had a 34% clearance rate. [ 62 ]  Advantages of ingenol mebutate treatment include the short duration of therapy and a low recurrence rate. [ 63 ]  Local skin reactions including pain, itching and redness can be expected during treatment with ingenol mebutate. This treatment was derived from the petty spurge,  Euphorbia peplus  which has been used as a traditional remedy for keratosis.


Topical  diclofenac sodium  gel is a nonsteroidal anti-inflammatory drug that is thought to work in the treatment of AK through its inhibition of the arachidonic acid pathway, thereby limiting the production of prostaglandins which are thought to be involved in the development of UVB-induced skin cancers. [ 40 ]  Recommended duration of therapy is 60 to 90 days with twice daily application. Treatment of facial AK with diclofenac gel led to complete lesion resolution in 40% of cases. [ 64 ]  Common side effects include dryness, itching, redness, and rash at the site of application. [ 64 ]


Topical  retinoids  have been studied in the treatment of AK with modest results, and the American Academy of Dermatology does not currently recommend this as first-line therapy. [ 65 ]  Treatment with  adapalene  gel daily for 4 weeks, and then twice daily thereafter for a total of nine months led to a significant but modest reduction in the number AKs compared to placebo; it demonstrated the additional advantage of improving the appearance of photodamaged skin. [ 66 ]


Topical  tretinoin  is ineffective as treatment for reducing the number of AKs. [ 25 ]  For secondary prevention of AK, systemic, low-dose  acitretin  was found to be safe, well tolerated and moderately effective in chemoprophylaxis for skin cancers in kidney transplant patients. [ 67 ]   Acitretin is a viable treatment option for organ transplant patients according to expert opinion. [ 48 ]


Tirbanibulin  (Klisyri) was approved for medical use in the United States in December 2020, for the treatment of actinic keratosis on the face or scalp. [ 68 ] [ 69 ] [ 70 ] [ 71 ]


Liquid nitrogen  (−195.8 °C) is the most commonly used destructive therapy for the treatment of AK in the United States. [ 72 ]  It is a well-tolerated office procedure that does not require anesthesia. [ 73 ]


Cryotherapy is particularly indicated for cases where there are fewer than 15 thin, well-demarcated lesions. [ 72 ]  Caution is encouraged for thicker, more hyperkeratotic lesions, as dysplastic cells may evade treatment. [ 57 ]   Treatment with both cryotherapy and field treatment can be considered for these more advanced lesions. [ 57 ]   Cryotherapy is generally performed using an open-spray technique, wherein the AK is sprayed for several seconds. [ 25 ]


The process can be repeated multiple times in one office visit, as tolerated. Cure rates from 67 to 99 percent have been reported, [ 74 ] [ 15 ]  depending on freeze time and lesion characteristics. Disadvantages include discomfort during and after the procedure; blistering, scarring and redness; hypo- or hyperpigmentation; and destruction of healthy tissue. [ 75 ]


AKs are one of the most common dermatologic lesions for which  photodynamic therapy , including topical  methyl aminolevulinate  (MAL) or  5-aminolevulinic acid  (5-ALA), is indicated. [ 76 ]


Treatment begins with preparation of the lesion, which includes scraping away scales and crusts using a dermal curette. A thick layer of topical MAL or 5-ALA cream is applied to the lesion and a small area surrounding the lesion, which is then covered with an occlusive dressing and left for a period of time. During this time the photosensitizer accumulates in the target cells within the AK lesion. The dressings are then removed and the lesion is treated with light at a specified wavelength.


Multiple treatment regimens using different photosensitizers, incubation times, light sources, and pretreatment regimens have been studied and suggest that longer incubation times lead to higher rates of lesion clearance. [ 77 ]  Photodynamic therapy is gaining in popularity. It has been found to have a 14% higher likelihood of achieving complete lesion clearance at 3 months compared to cryotherapy, [ 78 ]  and seems to result in superior cosmetic outcomes when compared to cryotherapy or 5-FU treatment. [ 79 ]  Photodynamic therapy can be particularly effective in treating areas with multiple AK lesions. [ 80 ]


Laser therapy  using  carbon dioxide  (CO 2 ) or erbium:yttrium aluminum garnet ( Er:YAG ) lasers is a treatment approach being utilized with increased frequency, and sometimes in conjunction with computer scanning technology. [ 83 ]  Laser therapy has not been extensively studied, but current evidence suggests it may be effective in cases involving multiple AKs refractive to medical therapy, or AKs located in cosmetically sensitive locations such as the face. [ 84 ]   The CO 2  laser has been recommended for extensive actinic cheilitis that has not responded to 5-FU. [ 57 ]


A  chemical peel  is a topically applied agent that wounds the outermost layer of the skin, promoting organized repair, exfoliation, and eventually the development of smooth and rejuvenated skin. Multiple therapies have been studied. A medium-depth peel may effectively treat multiple non-hyperkeratotic AKs. [ 85 ]  It can be achieved with 35% to 50%  trichloroacetic acid  (TCA) alone or at 35% in combination with  Jessner's solution  in a once-daily application for a minimum of 3 weeks; 70%  glycolic acid  (α-hydroxy acid); or solid CO 2 . [ 86 ]


When compared to treatment with 5-FU, chemical peels have demonstrated similar efficacy and increased ease of use with similar morbidity. [ 87 ]  Chemical peels must be performed in a controlled clinic environment and are recommended only for individuals who are able to comply with follow-up precautions, including avoidance of sun exposure. Furthermore, they should be avoided in individuals with a history of  HSV  infection or  keloids , and in those who are  immunosuppressed  or who are taking  photosensitizing  medications.


Untreated AKs follow one of three paths: they can either persist as AKs, regress, or progress to invasive skin cancer, as AK lesions are considered to be on the same continuum with  squamous cell carcinoma  (SCC). [ 17 ]  AK lesions that regress also have the potential to recur.


Given the aforementioned differering clinical outcomes, it is difficult to predict the clinical course of any given actinic keratosis.  AK lesions may also come and go—in a cycle of appearing on the skin, remaining for months, and then disappearing. Often they will reappear in a few weeks or months, particularly after unprotected sun exposure. Left untreated, there is a chance that the lesion will advance to become invasive.  Although it is difficult to predict whether an AK will advance to become squamous cell carcinoma, it has been noted that squamous cell carcinomas originate in lesions formerly diagnosed as AKs with frequencies reported between 65 and 97%. [ 17 ]


Actinic keratosis is very common, with an estimated 14% of dermatology visits related to AKs. [ 91 ]  It is seen more often in fair-skinned individuals, [ 33 ]  and rates vary with geographical location and age. [ 92 ]  Other factors such as exposure to ultraviolet (UV) radiation, [ 93 ]  certain  phenotypic  features, and immunosuppression can also contribute to the development of AKs.


Men are more likely to develop AK than women, and the risk of developing AK lesions increases with age. These findings have been observed in multiple studies, with numbers from one study suggesting that approximately 5% of women ages 20–29 develop AK compared to 68% of women ages 60–69, and 10% of men ages 20–29 develop AK compared to 79% of men ages 60–69. [ 94 ]


Geography seems to play a role in the sense that individuals living in locations where they are exposed to more UV radiation throughout their lifetime have a significantly higher risk of developing AK. Much of the literature on AK comes from Australia, where the prevalence of AK is estimated at 40–50% in adults over 40, [ 94 ]  as compared to the United States and Europe, where prevalence is estimated at under 11–38% in adults. [ 37 ] [ 93 ]  One study found that those who immigrated to Australia after age 20 had fewer AKs than native Australians in all age groups. [ 95 ]


Diagnostically, researchers are investigating the role of novel biomarkers to assist in determining which AKs are more likely to develop into cutaneous or metastatic SCC. Upregulation of  matrix metalloproteinases  (MMP) is seen in many different types of cancers, and the expression and production of MMP-7 in particular has been found to be elevated in SCC specifically. [ 96 ]  The role of  serin peptidase inhibitors  (Serpins) is also being investigated. SerpinA1 was found to be elevated in the keratinocytes of SCC cell lines, and SerpinA1 upregulation was correlated with SCC tumor progression  in vivo . [ 96 ]  Further investigation into specific biomarkers could help providers better assess prognosis and determine best treatment approaches for particular lesions.


In terms of treatment, a number of medications are being studied. Resiquimod is a TLR 7/8 agonist that works similarly to imiquimod, but is 10 to 100 times more potent; when used to treat AK lesions, complete response rates have range from 40 to 74%. [ 97 ]   Afamelanotide  is a drug that induces the production of melanin by  melanocytes  to act as a protective factor against UVB radiation. [ 98 ]  It is being studied to determine its efficacy in preventing AKs in organ transplant patients who are on immunosuppressive therapy.  Epidermal growth factor receptor  (EGFR) inhibitors such as  gefitinib , and anti-EGFR antibodies such as  cetuximab  are used in the treatment of various types of cancers, and are currently being investigated for potential use in the treatment and prevention of AKs. [ 99 ]


The  arrector pili muscles , also known as  hair erector muscles , [ 1 ]  are small muscles attached to  hair follicles  in  mammals . Contraction of these muscles causes the hairs to stand on end, [ 2 ]  known colloquially as  goose bumps  (piloerection). [ 3 ]


Each arrector pili is composed of a bundle of  smooth muscle  fibres which attach to several follicles (a follicular unit). [ 4 ]  Each is innervated by the sympathetic division of the  autonomic nervous system . [ 4 ]  The muscle attaches to the follicular stem cell niche in the follicular bulge, [ 3 ] [ 4 ] [ 5 ]  splitting at their deep end to encircle the follicle. [ 6 ]


The contraction of the muscle is involuntary. Stresses such as  cold ,  fear  etc. may stimulate the  sympathetic nervous system , and thus cause muscle contraction. [ 4 ]


Contraction of arrector pili muscles have a principal function in the majority of mammals of providing thermal insulation. [ 4 ]  Air becomes trapped between the erect hairs, helping the animal retain heat.


Many animals experience contraction of the arrector pili muscle in response to a perceived threat. This helps the animal seem more larger and more intimidating as a result. [ 7 ]


Pressure exerted by the muscle may cause  sebum  to be forced along the hair follicle towards the surface, protecting the hair. [ 8 ]


Arrector pili muscles also stabilise the base of the  hair follicle . [ 5 ] [ 6 ]


Skin conditions such as  leprosy  can damage arrector pili muscles, preventing their contraction. [ 9 ]  Inducing contraction of the arrector pili muscles via an  α1-adrenergic receptor  agonist has been shown to reduce hair shedding as a result of  traction alopecia [ 10 ]


The term "arrector pili" comes from Latin. It translates to "hair erector". [ 1 ]


Derm101  was an online and mobile resource for physicians and healthcare professionals to learn the diagnosis and treatment of dermatologic diseases. [ 1 ]  The resource includes online textbooks, interactive quizzes, peer-reviewed open access dermatology journals, a dermatologic surgery video library, case studies, thousands of clinical photographs and photomicrographs of skin diseases, and mobile applications.


Dr.  A. Bernard Ackerman  (1936–2008), a prominent figure in  dermatology  and  dermatopathology , and Andy Zwick, his nephew and collaborator, founded Derm101 in 2002. [ 2 ] [ 3 ]  The concept for Derm101 was envisioned and proposed to Dr. Ackerman by Zwick in 1999, while he was a senior at  Harvard , and they went on to develop Derm101 together. Derm101 debuted in February 2002 at the annual meeting of the  American Academy of Dermatology  in New Orleans.


In February 2016, Nestlé announced its creation of Nestlé Skin Health, a conglomerate of skin health-related companies, of which Derm101 was a part of. [ 4 ]  In 2019, Nestlé Skin Health was acquired by a private equity firm EQT, a unit of the Abu Dhabi Investment Authority and PSP Investments, and rebranded as Galderma. [ 5 ] [ 6 ]  Shortly after the sale was finalized, Galderma made the decision to decommission Derm101 which occurred on December 31, 2019.


• Derm101.com ( http://www.derm101.com )


Dr. Pimple Popper  is an American  reality television  series airing on  TLC . The series, starring  dermatologist  and Internet celebrity  Dr. Sandra Lee , follows her as she treats patients with unusual cases of facial and skin disorders at her clinic Skin Physicians & Surgeons in the  Inland Empire  city of  Upland, California . The show started with an hour-long special on January 3, 2018 before the first season aired on July 11, 2018. [ 1 ] [ 2 ] [ 3 ]


Initially airing at 10:00 p.m.  Eastern Time  on Wednesdays,  Dr. Pimple Popper  became the top-rated cable program in its time slot among women between ages 25–54. On August 14, the day before the final episode for Season 1 aired, TLC announced it had renewed the series for a second season, with new episodes set to air in January 2019. [ 4 ]  Another hour-long special was aired on December 13, 2018, before the second season began on January 3, 2019 with its episodes moved to 9 p.m. Eastern Time on Thursdays. Beginning part-way through the fifth season, new episodes became available on the  Discovery+  streaming service, before returning to TLC for the sixth season. A spin-off series titled  Dr. Pimple Popper: Before the Pop  premiered on September 3, 2020. [ 5 ]


The ninth and final season premiered on April 5, 2023. [ 6 ]


On August 5, 2020, it was announced that a spin-off series titled  Dr. Pimple Popper: Before the Pop  would premiere on September 3, 2020. [ 5 ]


Dr. Pimple Popper: This Is Zit  is an online series available on TLC's website and  Facebook . Each three- to six-minute episode focuses on a particular procedure done by Dr. Lee. [ 97 ] [ 98 ]


The first season of  Dr. Pimple Popper  has a  Rotten Tomatoes  rating of 78%. [ 99 ]  Kristen Baldwin of  Entertainment Weekly  gave the pilot episode a "B" rating, commenting that " Pimple Popper  delivers that blast of feel-good warmth you want from a makeover show, as the patients offer tearful post-procedural testimonials about how Dr. Lee changed their life for the better." [ 100 ]


Excess skin  is an effect of surplus skin and fat after expansion during  pregnancy  or  adipositas  and following a massive and considerable  weight loss . Further reasons can be aging effects, genetic disorders or an intentional expansion for skin reconstruction. Due to the elastic nature of the skin, there is generally some improvement over time. Excessive loose skin can be permanent to a degree but surgical treatment is an option.


Methods to remove excess skin by surgery include  abdominoplasty ,  breast reduction  and  brachioplasty .


In 1994,  60 Minutes  covered the mystery of Tomm Tennent, a young man "born hugely wrinkled by an excess of skin". Per  60 Minutes , Tennent was then the only person in the world with this congenital condition. [ 1 ]  He was born in 1992 with a great excess of skin, which hung about him in many wrinkles. As he grew towards adulthood, he "grew into" his skin, as into an oversize garment, and the wrinkles flattened out. His condition is compared to  Shar Pei  dog puppies, which have this condition also; the boy and Shar Pei puppies in their skins both have 10 times the normal level of  hyaluronic acid . [ 2 ]


In March 2015, Kaitlyn Smith shared her experience after losing 208 pounds ("half her size"), [ 3 ]  having once weighed more than 400 lbs.


In September 2020,  Biggest Loser  trainer Erica Lugo underwent a 360 tummy tuck. Having quickly lost over 160 lbs, Lugo was left with 8.5 lbs of excess skin.  People  covered the pre- and post- op experience. Lugo told  People  the decision to get surgery was not easy, but that she had a "new body" and was "floored" at the postoperative results. [ 4 ] [ 5 ]


TLC Skin Tight is a TV show with each episode following “two people who have lost massive amounts of weight and are about to undergo a full body transformation through skin removal surgery.” [ 6 ]  “It’s not unusual, says the show, for there to be “up to 50 pounds” of sagging skin following massive weight loss. Skin Tight ran for three seasons and 33 episodes, with the first episode airing 6 January 2016, and the last 20 May 2018. [ 7 ] [ non-primary source needed ]


First Derm  is a US-based online  dermatology  and tele-health website providing answers to skin conditions. Users send in cases to  board certified   dermatologists  via an  iOS ,  Android  or  Web app .


First Derm was founded in 2014 by Dr. Alexander Börve to support dermatologists in treating patients online. Dr. Börve studied at the  Sahlgrenska Academy  based in The  University of Gothenburg , where he was a researcher in  mobile health  and tele-dermatology. [ 1 ]  The research conducted was one of the first of its time, based on using mobile devices as a tool to answer questions and queries for dermatologists. The research included a pilot study of the effectiveness of a mobile health service in Sweden, [ 2 ]  the use of MMS and  SMS  in teledermatology, [ 3 ]  and the use of  teledermoscopy  as a tool to refer possible skin cancer patients to a dermatologist. [ 4 ]


Over 300,000 cases have been checked from over 160 countries and the service is available in seven languages.


The purpose of First Derm is to provide immediate solutions to skin care concerns without diagnosing the patient. This allows the patient to speed up the referral process and receive surgery or treatment more quickly than the traditional route.


The tool is also used by national health services such as  NHSx  who employ the tool as a triage solution for doctors. [ 5 ]


The  hair follicle  is an  organ  found in  mammalian   skin . [ 1 ]  It resides in the  dermal  layer of the skin and is made up of 20 different  cell types , each with distinct functions. The hair follicle regulates  hair growth  via a complex interaction between  hormones ,  neuropeptides , and  immune cells . [ 1 ]  This complex interaction induces the hair follicle to produce different types of  hair  as seen on different parts of the body. For example,  terminal hairs  grow on the  scalp  and  lanugo hairs  are seen covering the bodies of  fetuses  in the  uterus  and in some  newborn babies . [ 1 ]  The process of  hair growth  occurs in distinct sequential stages:  anagen  is the active growth phase,  catagen  is the regression of the hair follicle phase,  telogen  is the resting stage,  exogen  is the active shedding of hair phase and  kenogen  is the phase between the empty hair follicle and the growth of new hair. [ 1 ]


The function of hair in humans has long been a subject of interest and continues to be an important topic in society, developmental biology and medicine. Of all mammals, humans have the longest growth phase of scalp hair compared to hair growth on other parts of the body. [ 1 ]  For centuries, humans have ascribed esthetics to scalp hair styling and dressing and it is often used to communicate social or cultural norms in societies. In addition to its role in defining human appearance, scalp hair also provides protection from  UV sun rays  and is an insulator against extremes of hot and cold temperatures. [ 1 ]  Differences in the shape of the scalp hair follicle determine the observed ethnic differences in scalp hair appearance, length and texture.


There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include  alopecia [ 2 ]  or hair loss,  hirsutism  or excess hair growth and  lupus erythematosus . [ 3 ] [ 2 ]


The position and distribution of hair follicles varies over the body. For example, the skin of the palms and soles does not have hair follicles whereas skin of the scalp, forearms, legs and genitalia has abundant hair follicles. [ 1 ]  There are many structures that make up the hair follicle. Anatomically, the triad of hair follicle, sebaceous gland and arrector pili muscle make up the  pilosebaceous unit . [ 1 ]


A hair follicle consists of :


Other structures associated with the hair follicle include the cup in which the follicle grows known as the infundibulum, [ 8 ]  the  arrector pili  muscles, the  sebaceous glands , and the  apocrine   sweat glands .  Hair follicle receptors  sense the position of the hair.


Attached to the follicle is a tiny bundle of  muscle fiber  called the  arrector pili .  This muscle is responsible for causing the follicle lissis to become more perpendicular to the surface of the skin, and causing the follicle to protrude slightly above the surrounding skin (piloerection) and a  pore  encased with skin oil. This process results in  goose bumps  (or goose flesh).


Also attached to the follicle is a  sebaceous gland , which produces the oily or waxy substance  sebum . The higher the  density  of the hair, the more sebaceous glands that are found.


There are ethnic differences in several different hair characteristics. The differences in appearance and texture of hair are due to many factors: the position of the hair bulb relative to the hair follicle, size and shape of the dermal papilla, and the curvature of the hair follicle. [ 1 ]  The scalp hair follicle in people of European descent is elliptical in shape and, therefore, produces straight or wavy hair, whereas the scalp hair follicle of people of African descent is more curvy, resulting in the growth of tightly curled hair. [ 1 ]


(micrometers)


In utero, the epithelium and underlying  mesenchyme  interact to form hair follicles. [ 11 ] [ 12 ]


A key aspect of hair loss with age is the aging of the hair follicle.  Ordinarily, hair follicle renewal is maintained by the stem cells associated with each follicle.  Aging of the hair follicle appears to be primed by a sustained cellular response to the DNA damage that accumulates in renewing stem cells during aging. [ 13 ]   This damage response involves the proteolysis of type XVII collagen by neutrophil elastase in response to the DNA damage in the hair follicle stem cells.  Proteolysis of collagen leads to elimination of the damaged cells and then to terminal hair follicle miniaturization.


Hair grows in cycles of various phases: [ 14 ]   anagen  is the growth phase;  catagen  is the involuting or regressing phase; and  telogen , the resting or quiescent phase (names derived using the Greek prefixes ana-, kata-, and telos- meaning up, down, and end respectively).  Each phase has several morphologically and histologically distinguishable sub-phases.  Prior to the start of cycling is a phase of  follicular morphogenesis  (formation of the follicle).  There is also a shedding phase, or  exogen , that is independent of anagen and telogen in which one or several hairs that might arise from a single follicle exits.  Normally up to 85% of the hair follicles are in anagen phase, while 10–14% are in telogen and 1–2% in catagen. The cycle's length varies on different parts of the body. For  eyebrows , the cycle is completed in around 4 months, while it takes the  scalp  3–4 years to finish; this is the reason eyebrow hair have a much shorter length limit compared to hair on the head. Growth cycles are controlled by a chemical signal like  epidermal growth factor .  DLX3  is a crucial regulator of hair follicle differentiation and cycling. [ 15 ] [ 16 ]


Anagen is the active growth phase of hair follicles [ 17 ]  during which the root of the hair is dividing rapidly, adding to the hair shaft. During this phase the hair grows about 1 cm every 28 days. A hair pulled out in this phase will typically have the  root sheath  attached to it which appears as a clear gel coating the first few mm of the hair from its base; this may be misidentified as the follicle, the root or the sebaceous gland by non-health care professionals. Scalp hair stays in this active phase of growth for 2–7 years; this period is genetically determined. At the end of the anagen phase an unknown signal causes the follicle to go into the catagen phase.


The catagen phase is a short transition stage that occurs at the end of the anagen phase. [ 18 ]  It signals the end of the active growth of a hair. This phase lasts for about 2–3 weeks while the hair converts to a club hair, which is formed during the catagen phase when the part of the hair follicle in contact with the lower portion of the hair becomes attached to the hair shaft. A bulb of keratin attaches to the bottom tip of the hair and keeps it in place while a new hair begins to grow below it. A hair pulled out in this phase will have the bulb of keratin attached to it which appears as a small white ball on the end of the hair. This process cuts the hair off from its blood supply and from the cells that produce new hair. When a club hair is completely formed, about a 2-week process, the hair follicle enters the telogen phase.


The telogen phase is the resting phase of the hair follicle, about three months. [ 19 ]  When the body is subjected to extreme stress, as much as 70 percent of hair can prematurely enter the telogen phase and begin to fall, causing a noticeable loss of hair. This condition is called  telogen effluvium . [ 20 ]  The club hair is the final product of a hair follicle in the telogen stage, and is a dead, fully keratinized hair. [ 11 ]   Fifty to one-hundred club hairs are shed daily from a normal scalp. [ 11 ]


There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include  alopecia  or hair loss,  hirsutism  or excess hair growth, and  lupus erythematosus . [ 3 ]  Therefore, understanding the function of the normal hair follicle is fundamental to diagnosing and treating many dermatologic and systemic diseases with hair abnormalities. [ 3 ]  Studies of Witka et al. 2020 has shown the role of  microbiome  in the biology, immunology and diseases of scalp hair follicle. Studies further shown that change in hair follicle microbiome result into scalp disease like;  Seborrheic dermatitis  of the scalp and  dandruff ,  Folliculitis decalvans ,  Androgenetic alopecia ,  Scalp psoriasis  and  Alopecia areata . [ 21 ]


Hair follicles form the basis of the two primary methods of  hair transplantation  in  hair restoration ,  Follicular Unit Transplantation  (FUT) and  follicular unit extraction  (FUE). In each of these methods, naturally occurring groupings of one to four hairs, called follicular units, are extracted from the hair restoration patient and then surgically implanted in the balding area of the patient's scalp, known as the recipient area. These follicles are extracted from donor areas of the scalp, or other parts of the body, which are typically resistant to the miniaturization effects of the hormone  DHT . It is this miniaturization of the hair shaft that is the primary predictive indicator of  androgenetic alopecia , [ 22 ]  commonly referred to as male pattern baldness or male hair loss. When these  DHT -resistant follicles are transplanted to the recipient area, they continue to grow hair in the normal hair cycle, thus providing the hair restoration patient with permanent, naturally-growing hair.


While hair transplantation dates back to the 1950s, [ 23 ]  and plucked human hair follicle cell culture in vitro to the early 1980s, [ 24 ]  it was not until 1995 when hair transplantation using individual follicular units was introduced into medical literature. [ 25 ]


Hair removal  is the deliberate removal of  body hair  or head  hair . This process is also known as  epilation  or  depilation .


Hair is a common feature of the human body, exhibiting considerable variation in thickness and length across different populations. Hair becomes more visible during and after  puberty . Additionally, men typically exhibit thicker and more conspicuous body hair than women. [ 1 ]
Both males and females have visible body hair on the  head ,  eyebrows ,  eyelashes ,  armpits ,  genital area ,  arms , and  legs . Males and some females may also have thicker hair growth on their  face ,  abdomen ,  back ,  buttocks ,  anus ,  areola ,  chest ,  nostrils , and  ears . Hair does not generally grow on the  lips , back of the ear, the underside of the  hands  or  feet , or on certain areas of the  genitalia .


Hair removal may be practiced for cultural,  aesthetic ,  hygienic , sexual, medical, or religious reasons. Forms of hair removal have been practiced in almost all human cultures since at least the  Neolithic  era. The methods used to remove hair have varied in different times and regions.


The term "depilation" is derived from the  Medieval Latin  "depilatio," which in turn is derived from the  Latin  "depilare," a word formed from the prefix "de-" and the root "pilus," meaning "hair."


For centuries, hair removal has long shaped  gender roles , served to signify  social status  and defined notions of femininity and the ideal " body image ". [ 2 ] [ 3 ]  In early periods, the condition of being hairless was mostly done as a way to keep the body clean, using flint, seashells, beeswax and various other depilatory utensils and exfoliator substances, some highly questionable and highly caustic. [ 3 ] [ 4 ]   Ancient Rome  also associated hair removal with status: a person with smooth skin was associated with purity and superiority. Removing body hair was done by both men and women [ 2 ] [ 3 ] [ 5 ] [ 6 ]
Psilothrum or psilotrum ( Ancient Greek :  ψίλωθρον ) and dropax (Ancient Greek:  δρῶπαξ ) were depilatories in ancient Greece and Rome. [ 7 ] [ 8 ] [ 9 ]


In  Ancient Egypt , besides being a fashion statement for affluent Egyptians of all genders, [ 3 ] [ 10 ]  hair removal served as a treatment for  louse infestation , which was a prevalent issue in the region. [ 11 ]  Very often, they would replace the removed head hair with a  Nubian wig , which was seen as easier to maintain and also fashionable. [ 11 ]  Ancient Egyptian priests also shaved or depilated all over daily, so as to present a "pure" body before the images of the gods. [ citation needed ]


In ancient times, one highly abrasive depilatory paste consisted of an admixture of  slaked lime , water, wood-ash and yellow  orpiment  ( arsenic trisulfide ); In rural India and Iran, where this mixture is called  vajibt , it is still commonly used to remove  pubic hair . [ 3 ] [ 4 ] [ 12 ]  In other cultures, oil extracted from unripe olives (which had not reached one-third of their natural stage of ripeness) was used to remove body hair. [ 13 ]


During the  medieval period ,  Catholic  women were expected to let their hair grow long as a display of femininity, whilst keeping the hair concealed by wearing a  wimple  headdress in public places. [ 2 ]  The face was the only area where hair growth was considered unsightly; 14th-century ladies would also pick off hair from their foreheads to recede the hairline and give their face a more oval form. From the mid-16th century, it is said when Queen  Elizabeth I  came to power, she made  eyebrow  removal fashionable. [ 2 ]


By the 18th century, body hair removal was still considered a non-necessity by European and American women. But in 1760, when the first safety  straight razor  appeared for men to safely shave their beard and not inadvertently cut themselves, some women allegedly used this safety razor too. [ 2 ]  It was invented in Paris by the French master cutler  Jean-Jacques Perret  [ fr ] , author of  La pogonotomie, ou L'art d'apprendre à se raser soi-même  ( Pogonotomy , or The Art of Learning to Shave). [ 2 ]


It was not until the late 19th century that women in Europe and America started to make hair removal a component of their  personal care  regime. According to  Rebecca Herzig , the modern-day notion of body hair being unwomanly can be traced back to  Charles Darwin 's book first published in 1871 "The Descent of Man and Selection in Relation to Sex". Darwin's theory of natural selection associated body hair with "primitive ancestry and an atavistic return to earlier less developed forms", writes Herzig, a professor of gender and sexuality studies at Bates College in Maine. [ 2 ]  Darwin also suggests having less body hair was an indication of being more evolved and sexually attractive. [ 2 ]  As Darwin's ideas polarized, other 19th century medical and scientific experts started to link hairiness to "sexual inversion, disease pathology, lunacy, and criminal violence". Those connotations were mostly applied to women's and not men's body hair. [ 2 ]


By the early 20th century, the upper- and middle-class  white America  increasingly saw smooth skin as a marker of femininity, and female body hair as repulsive, with hair removal giving "a way to separate oneself from cruder people, lower class and immigrant". [ 2 ]


Harper's Bazaar , in 1915, was the first women's fashion magazine to run a campaign devoted to the removal of  underarm hair  as "a necessity". Shortly after,  Gillette  launched the first safety razor marketed specifically for women—the "Milady Décolleté Gillette", one that solves "...an embarrassing personal problem" and keeps the underarm "...white and smooth". [ 2 ]


Body hair characteristics such as thickness and length vary across human populations, some people have less pronounced  body hair  and others have more conspicuous body hair characteristics.


Each  culture  of human  society  developed  social norms  relating to the presence or absence of body hair, which has changed from one time to another. Different standards of  human physical appearance  and  physical attractiveness  can apply to females and males. People whose hair falls outside a culture's aesthetic  body image  standards may experience real or perceived  social acceptance  problems, psychological distress and  social pressure . For example, for women in several societies, exposure in public of body hair other than head hair, eyelashes and eyebrows is generally considered to be  unaesthetic , unattractive and  embarrassing . [ 14 ]


With the increased popularity in many countries of women wearing  fashion  clothing,  sportswear  and  swimsuits  during the 20th century and the consequential exposure of parts of the body on which hair is commonly found, there has emerged a popularization for women to remove visible  body hair , such as on legs, underarms and elsewhere, or the consequences of  hirsutism  and  hypertrichosis . [ 2 ] [ 15 ]  In most of the  Western world , for example, the vast majority of women regularly shave their legs and armpits, while roughly half also shave hair that may become exposed around their  bikini  pelvic area (often termed the "bikini line"). [ 2 ]


In Western and Asian cultures, in contrast to most Middle Eastern cultures, a majority of men are accustomed to shaving their facial hair, so only a minority of men reveal a  beard , even though fast-growing facial hair must be shaved daily to achieve a  clean-shaven  or beardless appearance. Some men shave because they cannot genetically grow a "full" beard (generally defined as an even density from cheeks to neck), their beard color is genetically different from their scalp hair color, or because their facial hair grows in many directions, making a  groomed  or contoured appearance difficult to achieve. Some men shave because their beard growth is excessive, unpleasant, or coarse, causing skin irritation. Some men grow a beard or  moustache  from time to time to change their appearance or visual style.


Some men  tonsure  or  head shave , either as a religious practice, a fashion statement, or because they find a shaved head preferable to the appearance of  male pattern baldness , or in order to attain enhanced cooling of the skull – particularly for people suffering from  hyperhidrosis . A much smaller number of Western women also shave their heads, often as a fashion or political statement.


Some women also shave their heads for cultural or social reasons. In India, tradition required widows in some sections of the society to shave their heads as part of being  ostracized  (see  Women in Hinduism § Widowhood and remarriage ). The outlawed custom is still infrequently encountered mostly in rural areas. Society at large and the government are working to end the practice of ostracizing widows. [ 16 ]  In addition, it continues to be common practice for men to shave their heads prior to embarking on a pilgrimage.


The  unibrow  is considered a sign of beauty and attractiveness for women in  Oman  and for both genders in  Tajikistan , often emphasized with  kohl . [ 2 ]  In Middle Eastern societies, regular trimming or removal of female and male  underarm hair  and pubic hair has been considered proper personal  hygiene , necessitated by local customs, for many centuries. [ 3 ] [ 17 ] [ 18 ]  Young girls and unmarried women, however, are expected to retain their body hair until shortly before marriage, when the whole body is depilated from the neck down. [ 3 ]


In China, body hair has long been regarded as normal, and even today women are confronted with far less  social pressure  to remove body hair. [ 2 ]  The same attitude exists in other countries in Asia. While hair removal has become routine for many of the continent's younger women, trimming or removing pubic hair, for instance, is not as common or popular as in the  Western world , [ 2 ]  where both women and men may trim or remove all their pubic hair for  aesthetic  or  sexual reasons . This custom can be motivated by reasons of potentially increased personal cleanliness or hygiene, heightened sensitivity during  sexual activity , or the desire to take on a more exposed appearance or visual appeal, or to boost  self-esteem  when affected by excessive hair. In Korea, pubic hair has long been considered a sign of fertility and sexual health, and it has been reported in the mid-2010s that some Korean women were undergoing pubic hair transplants, to add extra hair, [ 2 ]  especially when affected by the condition of pubic atrichosis (or  hypotrichosis ), which is thought to affect a small percentage of Korean women. [ 19 ]


Unwanted or excessive hair is often removed in preparatory situations by both sexes, in order to avoid any perceived  social stigma  or prejudice. For example, unwanted or excessive hair may be removed in preparation for an intimate encounter, or before visiting a public beach or swimming pool.


Though traditionally in Western culture women remove body hair and men do not, some women choose not to remove hair from their bodies, either as a non-necessity or as an act of rejection against  social stigma , while some men remove or trim their body hair, a practice that is referred to in modern society as being a part of "manscaping" (a  portmanteau expression  for  male-specific grooming ).


The term " glabrousness " also has been applied to human fashions, wherein some participate in culturally motivated hair removal by depilation (surface removal by  shaving ,  dissolving ), or  epilation  (removal of the entire hair, such as  waxing  or  plucking ).


Although the appearance of secondary hair on parts of the human body commonly occurs during  puberty , and therefore, is often seen as a symbol of adulthood, removal of this and other hair may become fashionable in some cultures and subcultures. In many modern  Western cultures , men are encouraged to shave their beards, and women are encouraged to remove hair growth in various areas. Commonly depilated areas for women are the underarms, legs, and pubic hair. Some individuals depilate the forearms. In recent years, bodily depilation in men has increased in popularity among some subcultures of Western males. [ citation needed ]


For men, the practice of depilating the pubic area is common, especially for aesthetic reasons. Most men will use a razor to shave this area, however, as best practice, it is recommended to use a body trimmer to shorten the length of the hair before shaving it off completely.


In ancient Egypt, depilation was commonly practiced, with  pumice  and  razors  used to shave. [ 20 ] [ 21 ]  In both  Ancient Greece  and  Ancient Rome , the removal of body and pubic hair may have been practiced among both men and women. It is represented in some artistic depictions of male and female nudity,  [ citation needed ]  examples of which may be seen in  red figure pottery  and sculptures like the  Kouros  of Ancient Greece in which both men and women were depicted without body or pubic hair. Emperor  Augustus  was said, by Suetonius, to have applied "hot nutshells" on his legs as a form of depilation. [ 22 ]


In the  clothes free movement , the term "smoothie" refers to an individual who has removed their body hair. In the past, such practices were frowned upon and in some cases,  forbidden: violators could face exclusion from the club. Enthusiasts grouped together and formed societies of their own that catered to that fashion, and smoothies became a major percentage at some nudist venues. [ 23 ]  The first Smoothie club (TSC) was founded by a British couple in 1991. [ 24 ]  A Dutch branch was founded in 1993 [ 25 ]  in order to give the idea of a hairless body greater publicity in the  Netherlands . Being a Smoothie is described by its supporters as exceptionally comfortable and liberating. The Smoothy-Club is also a branch of the World of the Nudest Nudist (WNN) and organizes nudist ship cruises and regular nudist events.


Head-shaving ( tonsure ) is a part of some  Buddhist ,  Christian ,  Muslim ,  Jain  and  Hindu  traditions. [ 26 ]  Buddhist and Christian  monks  generally undergo some form of tonsure during their induction into monastic life. [ citation needed ]


Within  Amish  society, tradition ordains men to stop shaving a part of their facial hair upon marriage and grow a  Shenandoah  style beard which serves the significance of wearing a  wedding ring ,  moustaches  are rejected as they are regarded as martial (traditionally associated with the  military ). [ 27 ]


In  Judaism  (see  Shaving in Judaism ), there is no obligation for women to remove body hair or facial hair, unless they wish to do so. However, in preparation for a woman's immersion in a  ritual bath  after concluding her days of purification (following her menstrual cycle), the custom of Jewish women is to shave off their pubic hair. [ 28 ]  During a  mourning  ritual, Jewish men are restricted in the  Torah  and  Halakha  to using scissors and prohibited from using a razor blade to shave their beards or sideburns, [ 29 ]  and, by custom, neither men nor women may cut or shave their hair during the  shiva  period. [ 30 ] [ 31 ]


The  Baháʼí Faith  recommends against complete and long-term head-shaving outside of medical purposes. It is not currently practiced as a law, contingent upon a future decision by the  Universal House of Justice , its highest governing body.  Sikhs  take an even stronger stance, opposing all forms of hair removal. One of the " Five Ks " of Sikhism is  Kesh , meaning "hair". [ 32 ]  Baptized Sikhs are specifically instructed to have unshorn Kesh (the hair on their head and beards for men) as a major tenet of the Sikh faith. To Sikhs, the maintenance and management of long hair is a manifestation of one's piety. [ 32 ]


The majority of Muslims believe that adult removal of pubic and axillary hair, as a hygienic measure, is religiously beneficial. Under Muslim law ( Sharia ), it is recommended to keep the beard. [ citation needed ]  A Muslim may trim or cut hair on the head. In the 9th century, the use of  chemical depilatories  for women was introduced by  Ziryab  in  Al-Andalus . [ citation needed ]


The body hair of surgical patients is often removed beforehand on the skin surrounding  surgical sites . Shaving was the primary form of hair removal until reports in 1983 showed that it may lead to an increased risk of infection.  [ 33 ]   Clippers  are now the recommended pre-surgical hair removal method. [ 34 ] [ 35 ]  A 2021  systematic review  brought together evidence on different techniques for hair removal before surgery. This involved 25 studies with a total of 8919 participants. Using a razor probably increases the chance of developing a surgical site infection compared to using clippers or hair removal cream or not removing hair before surgery. [ 36 ]  Removing hair on the day of surgery rather than the day before may also slightly reduce the number of infections. [ 36 ]


Some people with  trichiasis  find it medically necessary to remove ingrown eyelashes. [ 37 ]


The shaving of hair has sometimes been used in attempts to eradicate  lice  or to minimize  body odor  due to the accumulation of odor-causing  micro-organisms  in hair. In extreme situations, people may need to remove all body hair to prevent or combat infestation by  lice ,  fleas  and other parasites. Such a practice was used, for example, in  Ancient Egypt . [ 38 ]


It has been suggested that an increasing percentage of humans  removing  their pubic hair has led to reduced  crab louse  populations in some parts of the world. [ 39 ] [ 40 ]


A  buzz cut  or completely shaven haircut is common in military organizations where, among other reasons, it is considered to promote uniformity and neatness. [ 41 ] [ 42 ]  Most militaries have  occupational safety and health  policies that govern the hair length and hairstyles permitted; [ 41 ]  in the field and living in close-quarter environments where bathing and sanitation can be difficult, soldiers can be susceptible to parasite infestation such as  head lice , that are more easily propagated with long and unkempt hair. [ 43 ]  It also requires less maintenance in the field and in adverse weather it dries more quickly. Short hair is also less likely to cause severe burns from flash flame exposure (as a result of  flash fires  from  explosions ) which can easily set hair alight. [ 41 ]  Short hair can also minimize interference with safety equipment and fittings attached to the head, such as  combat helmets  and  NBC suits . [ 41 ]  Militaries may also require men to maintain clean-shaven faces as facial hair can prevent an air-tight seal between the face and  military gas masks  or other  respiratory  equipment, such as a  pilot's oxygen mask , or  full-face diving mask . [ 41 ]  The process of testing whether a mask adequately fits the face is known as a " respirator fit test ".


In many militaries, head-shaving (known as the  induction cut ) is mandatory for men when beginning their  recruit training . However, even after the initial recruitment phase, when head-shaving is no longer required, many soldiers maintain a completely or partially shaven hairstyle (such as a " high and tight ", " flattop " or " buzz cut ") for personal convenience or neatness. Head-shaving is not required and is often not permitted for women in military service, although they must have their hair cut or tied to regulation length. [ 42 ]  For example, the shortest hair a female soldier can have in the U.S. Army is 1/4 inch from the scalp. [ 44 ]


It is a common practice for professional  footballers (soccer players)  and  road cyclists  to remove leg hair for a number of reasons. In the case of a crash or tackle, the absence of the leg hair means the injuries (usually  road rash  or scarring) can be cleaned up more efficiently, and treatment is not impeded. Professional cyclists, as well as professional footballers, also receive regular leg  massages , and the absence of hair reduces the friction and increases their comfort and effectiveness. [ citation needed ]  Football players are also required to wear shin guards, and in case of a skin rash, the affected area can be treated more efficiently.


It is also common for  competitive swimmers  to shave the hair off their legs, arms, and torsos (and even their whole bodies from the neckline down), to reduce drag and provide a heightened "feel" for the water by removing the exterior layer of skin along with the body hair. [ 45 ]


In some situations, people's hair is shaved as a punishment or a form of humiliation. After World War II, head-shaving was a common punishment in France, the Netherlands, and Norway for women who had collaborated with the Nazis during the occupation, and, in particular, for women who had sexual relations with an occupying soldier. [ 46 ]


In the United States, during the  Vietnam War , conservative students would sometimes attack student radicals or "hippies" by shaving beards or cutting long hair. One notorious incident occurred at  Stanford University , when unruly fraternity members grabbed  Resistance  founder (and student-body president)  David Harris , cut off his long hair, and shaved his beard.


During European  witch-hunts  of the  Medieval  and  Early Modern periods , alleged  witches  were stripped naked and their entire body shaved to discover the so-called  witches' marks . The discovery of witches' marks was then used as evidence in trials. [ 47 ]


Inmates have their heads shaved upon entry at certain prisons. [ citation needed ]


"Depilation", or temporary removal of hair to the level of the skin, lasts several hours to several days and can be achieved by


"Epilation", or removal of the entire hair from the root, lasts several days to several weeks and may be achieved by


Electrology  has been practiced in the United States since 1875. [ 56 ]  It is approved by the  FDA . This technique permanently destroys germ cells [ citation needed ]  responsible for hair growth by way of the insertion of a fine probe into the hair follicle and the application of a current adjusted to each hair type and treatment area. [ citation needed ]  Electrology is the only permanent hair removal method recognized by the FDA. [ 57 ]


A 2006 review article in the journal "Lasers in Medical Science" compared intense pulsed light (IPL) and both alexandrite and diode lasers. The review found no statistical difference in effectiveness, but a higher incidence of side effects with diode laser-based treatment. Hair reduction after 6 months was reported as 68.75% for alexandrite lasers, 71.71% for diode lasers, and 66.96% for IPL. Side effects were reported as 9.5% for alexandrite lasers, 28.9% for diode lasers, and 15.3% for IPL. All side effects were found to be temporary and even  pigmentation  changes returned to normal within 6 months. [ 58 ]


A 2006 meta-analysis of randomized controlled trials found that alexandrite and diode lasers caused 50% hair reduction for up to 6 months, while there was no evidence of hair reduction from intense pulsed light, neodymium-YAG or ruby lasers. [ 59 ]


Many methods have been proposed or sold over the years without published clinical proof they can work as claimed.


There are several disadvantages to many of these hair removal methods.


Hair removal can cause issues: skin inflammation, minor burns, lesions, scarring, ingrown hairs, bumps, and infected hair follicles ( folliculitis ).


Some removal methods are not permanent, can cause medical problems and permanent damage, or have very high costs. Some of these methods are still in the testing phase and have not been clinically proven.


One issue that can be considered an advantage or a disadvantage depending upon an individual's viewpoint, is that removing hair has the effect of removing information about the individual's hair growth patterns due to  genetic  predisposition, illness,  androgen  levels (such as from pubertal hormonal imbalances or drug side effects), and/or  gender  status.


In the hair follicle, stem cells reside in a discrete microenvironment called the bulge, located at the base of the part of the follicle that is established during morphogenesis but does not degenerate during the hair cycle. The bulge contains multipotent stem cells that can be recruited during wound healing to help repair the epidermis. [ 61 ]


[ 62 ] == References ==


Hematidrosis , also called  hematohidrosis ,  haematidrosis ,  hemidrosis  and  blood sweat , is a very rare condition in which a human  sweats   blood . [ 1 ]  The term is from  Ancient Greek   haîma / haímatos  ( αἷμα / αἵματος ), meaning blood, and  hīdrṓs  ( ἱδρώς ), meaning sweat.


Blood usually oozes from the forehead, nails,  umbilicus , and other skin surfaces. In addition, oozing from  mucocutaneous  surfaces causing  nosebleeds , blood-stained tears, and vicarious menstruation are common. [ 2 ]  The episodes may be preceded by intense  headache  and abdominal pain and are usually self-limiting. In some conditions, the secreted fluid is more dilute and appears to be blood-tinged, while others may have darker, bright red secretions resembling blood. [ 3 ]


While the extent of blood loss generally is minimal, hematidrosis also results in the skin becoming extremely tender and fragile.


Hematidrosis is a condition in which  capillary  blood vessels that feed the  sweat glands  rupture, causing them to exude blood, occurring under conditions of extreme physical or emotional  stress . [ 4 ]  Severe mental  anxiety  activates the  sympathetic nervous system  to invoke the  fight-or-flight response  to such a degree as to cause hemorrhage of the vessels supplying the sweat glands. [ 5 ]  It has been suggested that acute fear and extreme stress can cause hematidrosis. [ 6 ]


Investigations such as  platelet  count, platelet aggregation test,  coagulation  profile, and  skin biopsy  reveal no abnormalities, and direct light microscopy of fluid demonstrates presence of normal  red blood cells . Investigations also fail to show any  vasculitis  or skin appendages (i.e.  sweat glands ,  sebaceous glands  and  hair follicles ) abnormalities. [ 3 ] [ 7 ]


A 2015 case study investigated hematidrosis with a patient who has  epilepsy . [ 8 ]


Effects on the body include weakness and mild-to-moderate dehydration from the severe anxiety and both blood and sweat loss. [ 9 ]


The condition is very rare, but there are reports in the medical literature of successful treatment with  beta blockers  ( propranolol  10 mg), [ 10 ] [ 11 ]  with significant reduction in the frequency of spontaneous blood oozing. The successful use of beta blockers supports the theory that the condition is induced by stress and anxiety. However, this etiology is not yet fully established, as the high prevalence of stress and anxiety in the modern era has not changed the incidence of this extremely rare disease, suggesting that other co-abnormalities also play a key role. [ 7 ]   Atropine  sulfate  transdermal patches  have also been used successfully. [ 3 ]


Favorable results with psychiatric counselling to reduce stress highlight the relationship between psychogenic causes and hematohidrosis. [ 5 ]


Dermatological research notes the presence of hematidrosis in people awaiting execution. [ 5 ]  It has also been proposed as a possible explanation for Jesus'  agony in the garden  of  Gethsemane  ( Luke 22:44 ), [ 12 ]  and for claims associated with  stigmata . [ 13 ] [ 14 ]


Leonardo da Vinci  described a soldier who sweated blood before battle. The phenomenon has also been observed in individuals in fear for their lives; a case occurred during the  London Blitz , and a case of fear of a storm while sailing, etc. [ 13 ]


Henle's layer  is the third and the outermost layer of the  inner root sheath  of the  hair  follicle, consisting of a single layer of  cubical cells  with clear flattened nuclei. It is named after  German   physician ,  pathologist  and  anatomist   Friedrich Gustav Jakob Henle . [ 1 ]


This article incorporates text in the  public domain  from  page 1068  of the 20th edition of   Gray's Anatomy   (1918)


The  history of dermatology  concerns the development of the practice of researching, defining and treating skin diseases, from  ancient times  to the  present . The field has its origin in the earliest forms of medicine, later becoming a distinct field with its own specialised practitioners and researchers.


Readily visible alterations of the  skin  surface have been recognised since the dawn of history. Among the first to take an interest in skin diseases were the  Mesopotamian peoples , who sought to understand the reasons for these problems, often resorting to explanations rooted in  religion ,  astrology  and  divination , and were the first to observe and define various dermatopathies. Skin conditions were considered a sign of divine punishment, the actions of demons and spirits, or as the result of black magic. [ 1 ] [ 2 ]


One of the most influential sources of understanding views on skin conditions in Mesopotamia comes from the  Babylonian  chief scholar  Esagil-kin-aplim , who wrote a diagnostic manual called  Sakikkū . One passage describes a complex skin condition which is associated with a sexual encounter. Another work,  Alandimmû , observes the human physical appearance, with a section dedicated to dermal marks, such as  moles , and  spots . [ 2 ]


While matching the descriptions of diseases in the few surviving  cuneiform  medical texts to specific ailments is challenging, it appears likely that Babylonians and  Assyrians  were the first to define and describe warts, pustules and scabies in writing. [ 3 ]  It is also possible to draw some conclusions about their attitude to skin conditions. Doctors of the era clearly sought to define disease according to certain criteria, using observations such as such as heat, smell, breath and bodily fluids, to help draw a  diagnostic  conclusion. [ 1 ] [ 2 ]


Among the oldest preserved medical documents relevant to skin diseases are the  ancient Egyptian   Smith Papyrus  and  Ebers Papyrus  dating to  c.  1600 BCE  and  c.  1550 BCE  respectively, though it is likely their contents were copied and passed down with their ultimate origins being much older  folk remedies . [ 4 ] [ 5 ]


These scrolls describe various diseases, including skin complaints such as  ulcers ,  burn wounds ,  rashes , and  tumours , as well as medical techniques on how to recognise and treat the diseases. Many of the treatments involved  magical incantations , the application of  herbs , or formulations of ingredients for medicines or ointments, as well as surgical procedures, such as  skin grafts . [ 6 ] [ 7 ]


Ancient Egyptians believed in a form of proto- humorism , that skin diseases were a symptom of health problems inside the body, caused by a blockage in the flow of bodily fluids. This turned the fluids into pain-making substances that could cause diseases anywhere in the body. [ 4 ]


While many of the procedures do not resemble those prescribed by modern medicine, the papyri are notable for their evidence of an early system of thorough inquiry into skin diseases, recommending a systematic examination, diagnosis and treatment, something that would later be more formalised by  Greek schools of medicine . [ 4 ] [ 7 ] [ 8 ]


Ancient Greek physicians adopted many treatments of the Egyptians, with the likes of  Homer  and  Diodorus  attesting to their respect of Egyptian medicine, though they rejected the use of incantations as a method of treatment. [ 8 ]  However, Greek and Roman medicine did not see the skin as an organ in itself, but rather a mere covering for the body. Similarly to the Egyptians, they viewed skin diseases as merely a representation of a humoral imbalance. [ 9 ]


Greek medicine, with its focus on the harmony between external beauty and internal goodness, laid the foundation for dermatological practices, emphasizing a healthy diet and physical activity.  Empedocles of Agrigento  made early inroads into understanding skin diseases and the concept of  cutaneous respiration , suggesting the skin's role in  gas exchange similar to the lungs . [ 10 ]


Hippocrates  described skin diseases and proposed the first classification of skin diseases with two categories: diseases of the skin itself (idiopathic) and diseases due to an imbalance of  humors  that a merely manifested on the skin (exanthematic). [ 11 ] [ 12 ]  Around a century later, his work would be compiled into the  Corpus Hippocraticum , which described the anatomy and physiological processes of the skin, including  sweating  and  glandular secretion . [ 12 ]


Rome, while indebted to Greek medical knowledge, also absorbed insights from  Etruscan  magical medicine, which revered water's regenerative powers and utilized plants for their  antiseptic  properties. Key Roman figures in dermatology include  Aulus Cornelius Celsus  and  Claudius Galen . Celsus, in his  De Medicina , detailed various skin conditions with precise terminology, covering diseases like  ulcers  and  leprosy . Galen expanded on dermatological diseases, especially those affecting the genitals, and explored the causes of hair color and the notion of  sexually transmitted diseases .


Much of early Greek and Roman medicinal research was preserved only as  Arabic-language  copies, stored in  Byzantine  libraries. [ 13 ]


Arab and Persian dermatologists made a significant contribution to the science during the Middle Ages, with clinicians of the  Islamic Golden Age  such as  Rhazes ,  Haly Abbas  and  Avicinna  providing descriptions of diseases, including  leprosy ,  vitiligo  and  smallpox . Avicinna wrote separate chapters in his  Canon of Medicine  on skin diseases, hair diseases and skin colour diseases. [ 13 ] [ 14 ]


In Europe, the Middle Ages saw the broader dissemination of ancient and foreign texts. Organised medicine was mostly the preserve of the  Catholic Church , which used such texts to inform its medical practice. [ 12 ]  For example, the  Benedictine  monk  Constantine the African  assembled a vast collection of medical works, which he translated into Latin and used to inform his teaching at the Abbey of  Monte Cassino , a major centre of learning in the 11th century. [ 15 ]


The arrival of Constantine in Italy in 1077 coincided with the rise in notoriety of the  Salerno Medical School , which had been founded in the 9th century, but was now increasingly influential.  Trota of Salerno  introduced new practices for treating the skin inspired by eastern societies [ 16 ]  and  Rogerius  first used the term  lupus  to describe the  malar rash ,  [ citation needed ]  with both physicians associated with the medical school. Rogerius in particular became renowned for his writing on the pathology and surgical treatment of diseases of the head, neck, trunk and extremities. [ 17 ]


The Middle Ages in Europe saw a marked rise in infectious skin diseases, such as leprosy and  plague , and the figures of  surgeons  and  barbers  (who, at the time, offered surgical interventions) emerging alongside physicians in the treatment of dermatological symptoms. [ 16 ]


The Renaissance period saw significant advancements in medical research. The previously taboo practice of postmortem dissection gradually became seen as necessary for the advancement of medicine. [ 18 ]


A major development in the formalisation of the study of skin came from  Andreas Vesalius , who first analysed and described the skin's substance, its layers, pores, fat and nerves. [ 9 ]  During his first public  anatomical dissection  in 1540, Vesalius showed and explained to the witnesses the difference between the 'inner skin' ( hypodermis ) and the 'outer skin' ( epidermis ) and their respective properties, [ 19 ]  and wrote about the subject in his seminal work on anatomy,  De Humani Corporis Fabrica Libri Septem  ("On the fabric of the human body in seven books").


In 1572,  Geronimo Mercuriali  completed  De morbis cutaneis  ("On the diseases of the skin"), which sought to compile all medical knowledge on skin diseases and was the first scientific work to be dedicated entirely to dermatology. Unlike Vesalius, much of his writing relied on ancient sources of dubious veracity, and did not attempt to test those assumptions with original research. [ 18 ]  While Mercuriali was a generalist physician, he went on to write many texts focused on skin diseases, as well as  De Decoration Liber  ("Book on Adornment") about the use of cosmetics, such as to hide blemishes.


There are many physicians which could be described as 'the first' dermatologist, such as English surgeon  Daniel Turner . He wrote a treatise of skin diseases in 1714 called De Morbis Cutaneis, A Treatise of Diseases Incident to the Skin in Two Parts. Despite its Latin title and unusually for medical texts at the time, Turner wrote the book in English, and it was soon translated into French and German. He combined ancient descriptions of diseases and their treatments with references to research by contemporaries such as  William Cowper , though Turner mostly recounts various cases that he encountered and how he treated them. [ 18 ]


Turner's writing did not yet approach the scientific standard of modern medicine. He blamed humours for discolourations in the skin, and wrote on how pregnant women could inflict marks and deformities on their unborn children due to the "strong imagination or disappointed longings of the mother". [ 20 ]  This last theory was a particular point of criticism used against Turner, with  Thomas Bateman  referring to him as "credulous". [ 18 ]


In 1799,  Francesco Bianchi  wrote the book  Dermatologia  which is the first comprehensive textbook of modern dermatology written for the students of medicine. [ 21 ]


The development of optics allowed medical researchers to look at diseased skin in more detail.


In 1801 the first great school of  dermatology  became a reality at the famous  Hôpital Saint-Louis  in Paris, while the first textbooks (Willan's, 1798–1808) and atlases ( Alibert's , 1806–1814) appeared in print during the same period of time. [ 22 ]


By the mid-19th century, dermatology had become a widely recognised field. [ 23 ]  Publications such as  Gustav Simon 's  Die Hautkrankheiten durch anatomische Untersuchungen erläutert  (Skin Diseases Illustrated by Anatomical Investigations) [ 24 ]  and  Ferdinand von Hebra 's  Atlas der Hautkrankheiten  (Atlas of Skin Diseases) [ 25 ]  sought to illustrate a wide range of dermatological conditions and allow physicians to recognise symptoms in their patients. Hospitals such as  Berlin's Charité  had established dedicated dermatological departments, which led to significant advances in the description of conditions and their potential treatments.


Hypnodermatology  is an informal label for the use of  hypnosis  in treating the skin conditions that fall between conventional medical  dermatology  and the mental health disciplines.


The use of hypnosis to provide relief for some skin conditions is based on observations that the severity of the disease may correlate with emotional issues. In addition,  hypnotherapy  has been used to suggest improvement on dermatological symptoms, such as chronic  psoriasis , [ 1 ]  eczema, [ 2 ]  ichthyosis, warts [ 3 ]  and  alopecia areata . [ 4 ]


Philip D. Shenefelt, a research  dermatologist  at the  University of South Florida School of Medicine , has identified two dozen dermatologic conditions that have shown response to hypnosis in the literature, with varying degrees of evidence. These include successful results in controlled trials on  verruca vulgaris ,  psoriasis , and  atopic dermatitis . [ 5 ] [ 6 ]  A 2005 review in the Mayo Clinic Proceedings stated that, "A review of the use of hypnosis in dermatology supports its value for many skin conditions not believed to be under conscious control". [ 7 ]  The most comprehensively studied skin conditions in relation to hypnotherapy are psoriasis and warts. [ 3 ]  Hypnosis may have positive effects on dermatological conditions in both adults and children. [ 8 ]


Hypnotherapy may contribute towards reducing itching and discomfort brought on by the presence of warts and improves and possibly decreasing lesions. [ 3 ]


This article about  alternative medicine  is a  stub . You can help Wikipedia by  expanding it .


Immunodermatology  studies  skin  as an organ of  immunity  in health and disease. Several areas have special attention, such as photo-immunology (effects of  UV  light on skin defense),  inflammatory  diseases such as  Hidradenitis suppurativa ,  allergic  contact  dermatitis  and  atopic eczema , presumably  autoimmune  skin diseases such as  vitiligo  and  psoriasis , and finally the  immunology  of  microbial  skin diseases such as  retrovirus  infections and  leprosy . New therapies in development for the  immunomodulation  of common immunological skin diseases include  biologicals  aimed at neutralizing  TNF-alfa  and  chemokine receptor  inhibitors. [ citation needed ]


There are multiple universities currently do Immunodermatology:


Metal allergies inflame the skin after it has been in contact with metal. They are a form of  allergic contact dermatitis . They are becoming more common, as of 2021 [update] , except in areas with regulatory countermeasures.


People may become sensitized to certain metals by skin contact, usually by wearing or holding consumer products (including non-metal products, like textiles and leather treated with metals), or sometimes after exposure at work. Contact with damaged skin makes sensitization more likely. Medical implants may also cause allergic reactions. Diagnosis is by  patch test , a method which does not work as well for metals as it does for some other allergens.


Prevention and treatment consists of avoiding the metal allergen; there is no other treatment, as of 2021 [update] . It can be difficult to identify and avoid the allergen, because many metals are common in the environment, and some are biologically necessary to humans. Regulations have successfully reduced the rates of some metal allergies in Europe, but are not widespread. The social and economic costs of metal allergies are high.


Metal allergies are  type IV allergies ; the metals are  haptens . The toxicity of some allergenic metals may contribute to the development of allergies. [ 1 ]


Nickel allergy  and allergies to  mercury  and  chromium  have long been recognised;  gold ,  palladium , and  cobalt  have gotten attention more recently. [ 2 ] [ 3 ]  There is often cross-sensitization, where a person allergic to one metal may become allergic to another, but monosensitization, reacting to just one metal, is also possible. [ 4 ]  For instance, many people allergic to nickel are often also allergic to cobalt (a similar element often found in the same places as nickel) and palladium. But it is also possible to only be allergic to one of these metals. [ 1 ]


Nickel is one of the most common contact allergens. [ 5 ]


Most cases of metal allergy are caused by consumer products containing metal; exposure at work can also cause metal allergies. [ 3 ]  The largest human exposure to metals is ingestion; while food or drink containing metals can cause an allergic reaction in people who already have an allergy, it's not clear if it can cause a new allergy, as of 2021 [update] . Some metal allergens are nutritionally necessary to humans. Airborne metals have been linked to higher rates of sensitization. [ 1 ]


It can be difficult to figure out what allergen a person with contact dermatitis is reacting to, especially if the allergic reaction is systemic, rather than just occurring where the allergen entered the body. [ 7 ]


Consumer products that have induced allergies include jewellery (both cheap and expensive, brand-name jewellery may release metal allergens [ 8 ] ), buttons, clothing fasteners (such as zippers, [ 1 ]  buckles, and hooks), dental restorations, mobile phones, and leather [ 3 ]  (from the  tanning  process). Metal hair fasteners may also leach allergens. [ 8 ]  The increase in consumer products, including consumer electronics, that use  metal nanomaterials , mainly silicon, titanium, zinc and aluminum, increases exposure. [ 1 ]


Tattoo inks  contaminated with metal allergens have been known to cause severe reactions, sometimes years later, when the original ink is not available for testing. [ 1 ]


Implants and prosthetics, including dental repairs, are also an exposure; dental work is the main way in which the general population is sensitized to palladium, and dental workers may get occupational palladium allergies, though cross-sensitization may also be a common way in which people develop an allergy to this fairly rare metal. Medications containing metals could also potentially cause sensitization. [ 1 ]


Exposure on damaged skin, such as chapped hands or a piercing, increases the risk of sensitization from a low-level exposure to the allergen. [ 1 ]


Diagnosis is by  patch testing , a method first used in 1895. Patches containing potential allergens are stuck on the skin, and the skin is monitored for inflammation. For metal allergens, patch test reproducibility is low, and the extent to which they predict implant failures is debated. If the person being tested has a rash already, it may be difficult to do a patch test. Patch testing may also worsen the allergy. it is also difficult to distinguish co-sensitivity from cross-sensitivity using a patch test. [ clarification needed ] [ 1 ]


In-vitro  tests, where a  blood sample  is examined for metal-sensitive T cells, are in development, but not widely used, partly due to cost. Many non-allergic people also have metal-specific T cells, and in some cases they seem to have more than some allergic individuals, which makes the test less useful. [ 1 ]


Metal allergies are rapidly becoming more common. Nickel is the most common contact allergen worldwide (of people with contact dermatitis, 11.4% in Europe, 8.8–25.7% in China, and 17.5% in North America are allergic to nickel). [ 1 ]


Nickel allergy, and contact allergies more generally, can develop when people are any age, but they are most likely to develop in early adulthood. This may be due to patterns in exposure or changes in the immune system with age, or both. [ 1 ]


Preventing and treating contact allergies largely involves avoiding the allergen, which may be difficult when it is a common metal. There are no other treatments for metal allergies, as of 2021 [update] . [ 1 ]


In the  Netherlands , regulations that limit the release of nickel from consumer products, introduced in the 1990s, [ 1 ]  worked. Dutch women are now significantly less likely to develop nickel allergies. [ clarification needed ] [ 3 ]  Sweden followed in 1994, and later [ when? ]  regulations were made Europe-wide. These limits cover objects inserted into piercings (0.2 μg/cm²/week) and those in direct or prolonged contact with the skin (0.5 μg/cm 2 ). They also set target values for nickel in ambient air; (20 ng/mg 3 ) increases in nickel concentrations in ambient air, even when absolute levels are quite low, have been linked to increased rates of sensitization in human populations. Nickel allergy rates in Europe have decreased, though it is still the most common contact allergy. [ 1 ]  Regulation is generally inadequate, given the amount of the social and economic harm caused by metal allergies. [ 1 ]


Regulation encouraged use of metals other than nickel, and that caused more cases of allergies to other metals. Nickel remains the most common, but cobalt is the second most common allergy, and in 2020 the EU introduced a temporary generic concentration limit (GCL) of 0.1% on cobalt. Limits on nickel and cobalt in textiles (130mg/kg nickel, 110 mg/kg cobalt) and leather (70mg/kg nickel, 60 mg/kg cobalt), were proposed in 2020 by France and Sweden. There is no allergen regulation of pallidium in Europe as of October 2021 [update] . [ 1 ]


MoleMax  was the first digital epiluminescence microscopy ( dermatoscopy ) system developed in cooperation with medical faculty Department of Dermatology [ 1 ]  of the  Medical University of Vienna . It is currently owned and distributed by DermaMedicalSystems. [ 2 ]


In 1997, MoleMax was presented to international experts at the Melanoma World Congress and the following Dermatology World Congress in  Sydney  and generated great public interest. Since then, over 2000 MoleMax systems are in use in over 50 countries.
Today, MoleMax is worldwide accepted clinical standard in digital  epiluminescence microscopy .


Thanks to the worldwide patented [ 3 ]   light polarisation  technique for cameras with skin contact, these camera systems do not require any immersion fluid for the epiluminescence microscopic analysis.


The MoleMax system was part of multiple scientific works such as measurements of the growth rate of pigmented  skin lesions
 [ 4 ] [ 5 ]
and verification of follow-up imaging. [ 6 ]
Images made by this system also ended up in large public image databases such as HAM10000. [ 7 ]


Polymorphous light eruption  ( PLE )  presents with  itchy   red   small bumps  on sun-exposed skin, particularly face, neck, forearms and legs. [ 1 ]  It generally appears 30 minutes to a few hours after sun exposure and may last between one and 14 days. [ 3 ]   The bumps may become  small blisters  or plaques and may appear bloody, [ 3 ] often healing with minimal scarring. [ 3 ]


It is a non-life-threatening and potentially distressing [ 4 ]  skin condition that is triggered by  sunlight  and artificial  UV exposure [ 5 ]  in a genetically susceptible person, [ 6 ]  particularly in  temperate climates  during the spring and early summer. [ 2 ]  Due to its many  clinical appearances , it is named polymorphic or polymorphous and the terms are used interchangeably. [ 7 ]  The resulting itch can cause significant suffering. [ 4 ] [ 8 ]


PLE is also defined as an idiopathic primary  photodermatosis , [ 9 ]  in which the  photosensitizer  is unknown. [ 4 ]


Treatments include prevention with sun avoidance and supervised light therapy, and symptom control with topical steroids. [ 4 ]


Typically, the first episode develops in the spring following the first exposure to intense sun. [ 10 ]  Further episodes of the irritable rash occur several hours to days following subsequent sun exposure. [ 11 ]


PLE appears on areas of the skin newly exposed to sunlight such as the visible part of the neckline, backs of hands, arms and legs, and feet, but less commonly the face. [ 2 ] [ 6 ]  At these areas, there may be feelings of burning [ 9 ]  and severe itching. Smooth red-topped small  papules  which merge into plaques, small fluid-filled blisters (papulovesicles) [ 2 ]  and less commonly target-shaped lesions which look like  erythema multiforme  may be visible. [ 5 ]  In addition, it may occur in other parts of the body in some people treated for inflammatory skin diseases with  phototherapy . [ 2 ]


The rash is usually quite symmetrical and characteristic for each individual, appearing similar with each recurrence, but can look dissimilar in different people. [ 10 ]


Fever, fatigue and headaches have been previously associated with the eruption, but are rare. [ 2 ]


The rash may persist for many days to a couple of weeks, [ 5 ]  resolving spontaneously without scarring as long as further sunlight exposure is avoided. [ 2 ]


Recurring yearly, the eruption can sometimes last longer than a few days if persistent and repeated sun exposure occurs. [ 2 ]  However, the "hardening" effect, with respite during the later summer, frequently occurs with gradual exposure of sunlight, [ 5 ]  eventually leading to significant improvement. [ 2 ]


The cause of PLE is not yet understood, but several factors may be involved. [ 6 ]  It is thought to be due to a  type IV delayed-type hypersensitivity  to an allergen produced in the body following sunlight exposure, [ 12 ]  in a genetically susceptible person. [ 10 ]  It is also thought that skin microbiome or microbial elements could be involved in pathogenesis of the disease  [ 13 ] [ 14 ]


PLE can be provoked by UVA or UVB (chief cause of sunburn) rays, meaning it can be triggered even by sunlight through glass. UV-A is a major constituent of sunlight, can pass through glass, is relatively resistant to sunscreen and can cause light eruption without sunburn. [ 2 ]


Artificial UV light sources from tanning units and phototherapy treatment units can also trigger PLE. About three-quarters of patients acquire PLE after UV-A exposure only, one-tenth after UV-B exposure only, and the rest after a combination of UV-A and UV-B exposure. [ 6 ]


People vary in the amount of sun exposure needed to trigger the rash. [ 15 ]


Oxidative stress  and the modification of the  redox  status of the skin has been implicated in the expression of PLE. [ 6 ]


It has been suggested that an undefined endogenous or exogenous photo-allergen may trigger a delayed immune reaction resulting in PLE. [ 6 ]


Half of patients have a family history of PLE, [ 6 ]  demonstrating a clear genetic influence. [ 16 ]


The preponderance in women with a decline in severity following menopause has been thought to be associated with oestrogen effects, [ 6 ]  A natural fall in oestrogens may account for the tendency to remit after the menopause. [ 9 ]


The diagnosis of PLE is typically made by assessing the history and clinical observations. Any investigations are usually to exclude other conditions, particularly  lupus  and  porphyria . [ 9 ]


Blood tests are usually normal. However, positive  antinuclear antibody  and  extractable nuclear antigen  (anti-Ro/La) in low titre may be found, even in the absence of other criteria to suggest a diagnosis of lupus erythematosus. If clinical findings suggest a possibility of porphyria, urinary and red cell porphyrin screening may be performed and are negative in PLE. [ 2 ]


Photoprovocation tests are usually not required but may be undertaken by specialised centres in winter. [ 2 ]  When a decision to undertake this is made, a small area of the frequently affected skin is exposed to varying doses of UVA and minimal erythema dose (MED) (amount of UV radiation that will produce minimal redness of skin within a few hours following exposure) [ 2 ] [ 17 ]  of broadband UVB for three consecutive days. An examination of the skin to detect the rash is made, however, up to 40% have  false negative  responses. [ 2 ]


Depending on the clinical signs,  histology  of a  skin biopsy  may vary. There may be oedema in the  epidermis  with a dense superficial and deep lymphocytic infiltrate [ 10 ]  without vasculitis. Recently appearing lesions may show  neutrophils .  Spongiosis  and vesicle formation may also be present.  Direct immunofluorescence  testing is negative. [ 2 ]


The photosensitivity connected with lupus erythematosus is the main condition that may appear like PLE. However, the rash of lupus is inclined to be more persistent. [ 2 ]  PLE does not increase the risk of lupus. [ 15 ]


Other similar appearing conditions are  solar urticaria , which has a shorter duration, the eczema-like condition, photosensitive dermatitis, [ 2 ]  and photosensitivity drug reaction. [ 9 ]


Prickly heat, which is caused by warm weather or heat is not the same as PLE. [ 5 ]


Photosensitivity is also found in some of the  porphyrias . Nearly all cases of  porphyria cutanea tarda [ 18 ]  exhibit blister formation on the skin within 2–4 days of light exposure.  Variegate porphyria [ 19 ]  and  hereditary coproporphyria [ 20 ]  can also exhibit symptoms of light-induced blisters. [ 18 ]


Sunlight has been documented to trigger numerous skin conditions and the confusing terminology and categorisation previously has made the correct diagnosis and subsequent treatment difficult. [ 4 ]


Variants of PLE have been described: [ 21 ] [ 12 ]


Management entails regulating triggers whilst simultaneously inducing "hardening"; that is, steadily increasing exposure to sunlight, [ 2 ]  as light sensitivity is reduced with repeated sun exposure [ 15 ]


Covering up with densely woven clothing has also been shown to help, in addition to applying a broad-spectrum, water-resistant semi-opaque sun protection factor (SPF) 50+  sunblock cream  before sun exposure and then every two hours thereafter confers some protection. [ 2 ]


The application of  topical corticosteroids  may lessen the redness and itch, [ 2 ]  and for preventing predictable holiday flare-ups, short courses of oral corticosteroids are sometimes considered. [ 2 ]


Another treatment option is a supervised course of low dose phototherapy, usually undertaken in winter. [ 2 ]  If resistant, the administration of  hydroxychloroquine  in early spring is sometimes considered. [ 10 ]


As sun exposure is avoided,  vitamin D  levels may fall and hence supplements are sometimes advised. [ 22 ]


Generally, PLE resolves without treatment; also, PLE irritations generally leave no scar. [ 15 ]


There may be a possible link with autoimmune thyroid disease. [ 9 ]  Some progression to autoimmune disease has been observed. [ 23 ]  However, another study of people with elevated titres of antinuclear antibodies with PLE found no progression to lupus erythematosus after an 8-year follow-up. [ 16 ]


In the United States, whilst one-quarter of people being investigated for a photosensitivity disorder were diagnosed with PLE, the prevalence in the general population is 10 to 15% and may even be as high as 40% as suggested in one study of more than 2000 people. [ 5 ] [ 6 ]  It is also particularly more prevalent in Central Europe and Scandinavia. [ 4 ]


PLE is more common in young adults and has a female preponderance [ 5 ]  with a ratio of 2:1 female-to-male. In Germany the female to male ratio has been cited as 9:1. [ 4 ]  It can, however, occur in all age groups and all skin types. [ 6 ]


Those experiencing sun exposure all year round seldom acquire PLE eruption. [ 15 ]  Hence, it is less common near the equator. [ 16 ]


The cases of this condition are most common between the spring and autumn months in the  northern hemisphere  and at higher altitudes. [ 12 ]


Reports of psychological distress have been made in more than 40% of peoples with PLE. [ 16 ]  This includes emotional distress, anxiety and depression [ 12 ]


Thomas Bateman , following on from findings of his predecessor,  Robert Willan , [ 24 ]  first recorded a description of PLE in the nineteenth century, defining it as  eczema solare  with recurrent non scarring eczematous lesions triggered by sun exposure. [ 25 ] [ 26 ]


Danish physician  Carl Rasch  first described the  eczema-like polymorphic light eruption  in 1900, following his interest in the effect of  sunlight  on the  skin . He has since been credited with coining the term "polymorphic light eruption". [ 27 ] [ 28 ]


Psychodermatology  is the treatment of  skin  disorders using  psychological  and  psychiatric  techniques by addressing the interaction between mind and skin. Though historically there has not been strong scientific support for its practice, there is increasing evidence that behavioral treatments may be effective in the management of chronic skin disorders. [ 1 ]


The practice of psychodermatology is based on the complex interplay between neurological, immunological, cutaneous and endocrine systems, known alternatively as the NICE network, NICS, and by other similar acronyms. The interaction between nervous system, skin, and immunity has been explained by release of mediators from network. In the course of several inflammatory skin diseases and psychiatric conditions, the neuroendocrine-immune-cutaneous network is destabilized.


The disorders that proponents classify as psychodermatologic fall into three general categories: psychophysiologic disorders, primary psychiatric disorders and secondary psychiatric disorders. [ 2 ]  Proponents frequently claim treatment for  psoriasis ,  eczema ,  hives , genital and oral  herpes ,  acne ,  warts , skin  allergies ,  pain , burning sensations, and hair loss. Psychodermatological treatment techniques include  psychotherapy ,  meditation , relaxation,  hypnosis ,  acupuncture ,  yoga ,  tai chi , and  anti-anxiety drugs . [ 3 ] [ 4 ] [ 5 ] [ 6 ]  Additionally, cosmetics companies may offer products utilizing terms such as "psychodermatology" or "neurocosmetics" in their marketing, [ 7 ]  though these terms are not regulated.


Psychophysiologic disorders are conditions that are precipitated by or worsened by experiencing stressful emotions. [ 8 ]  These conditions are not always related to stress and in many cases respond to medication but stress can be a contributing factor in some cases. [ 9 ]


In a 2013 paper published in the  Clinics in Dermatology , the official journal of the International Academy of Cosmetic Dermatology, the facts and controversies of this topic were examined with the conclusion: [ 1 ]