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84-428: Sun tanning or tanning is the process whereby skin color is darkened or tanned. It is most often a result of exposure to ultraviolet (UV) radiation from sunlight or from artificial sources, such as a tanning lamp found in indoor tanning beds. People who deliberately tan their skin by exposure to the sun engage in a passive recreational activity of sun bathing . Some people use chemical products that can produce
168-519: A common ancestor who lived around 200,000 years ago in Africa. Comparisons between known skin pigmentation genes in chimpanzees and modern Africans show that dark skin evolved along with the loss of body hair about 1.2 million years ago and that this common ancestor had dark skin. Investigations into dark-skinned populations in South Asia and Melanesia indicate that skin pigmentation in these populations
252-481: A "fair/medium/olive" context. Oculocutaneous albinism (OCA) is a lack of pigment in the eyes, skin and sometimes hair that occurs in a very small fraction of the population. The four known types of OCA are caused by mutations in the TYR , OCA2 , TYRP1 , and SLC45A2 genes. In hominids , the parts of the body not covered with hair, like the face and the back of the hands, start out pale in infants and turn darker as
336-401: A health benefit in reduced sunlight if there were limited sources of vitamin D. Hence the leading hypothesis for the evolution of human skin color proposes that: The genetic mutations leading to light skin, though partially different among East Asians and Western Europeans , suggest the two groups experienced a similar selective pressure after settlement in northern latitudes. The theory
420-510: A nearly colorless pigmentation, which may appear white. In 1975, Harvard dermatologist Thomas B. Fitzpatrick devised the Fitzpatrick scale to describe the common tanning behavior of various skin types, as follows: Dark skin does provide some protection against the sun’s ultraviolet rays, but it is a myth that people with dark skin tones are immune to the harmful effects of UV radiation. The most common risk of exposure to ultraviolet radiation
504-511: A number of the most prominent light-skin tone gene variants found in modern Europeans being introduced by Anatolian Neolithic Farmers that migrated into Europe beginning around 9,000 years ago, with selection pressure for lighter skin intensifying from the Neolithic period onwards. Research by Nina Jablonski suggests that an estimated time of about 10,000 to 20,000 years is enough for human populations to achieve optimal skin pigmentation in
588-410: A particular geographic area but that development of ideal skin coloration may happen faster if the evolutionary pressure is stronger, even in as little as 100 generations. The length of time is also affected by cultural practices such as food intake, clothing, body coverings, and shelter usage which can alter the ways in which the environment affects populations. Population and admixture studies suggest
672-522: A particular need for this thermoregulation since unlike other mammals they lack a carotid rete that allows precooling of blood to the brain, an organ extremely sensitive to changes in body temperature. Given endurance running and its needs for thermoregulation arose with H. erectus , this links hairlessness with the origin of H. erectus about 2 million years ago. As hominids gradually lost their fur between 1.2 and 4 million years ago, to allow for better cooling through sweating, their naked skin
756-608: A peak in Europe with around 28% of the population having at least one allele of one of the variations. A study of self-reported tanning ability and skin type in American non- Hispanic Caucasians found that SLC24A5 Phe374Leu is significantly associated with reduced tanning ability and also associated TYR Arg402Gln (rs1126809 ), OCA2 Arg305Trp (rs1800401 ) and a 2- SNP haplotype in ASIP (rs4911414 and rs1015362 ) to skin type variation within
840-434: A pink to red hue is found in particularly large quantities in red hair , the lips, nipples, glans of the penis, and vagina. Both the amount and type of melanin produced is controlled by a number of genes that operate under incomplete dominance . One copy of each of the various genes is inherited from each parent. Each gene can come in several alleles , resulting in the great variety of human skin tones. Melanin controls
924-864: A range of populations. This variation is ubiquitous in European populations but extremely rare elsewhere and shows strong signs of selection. The TYR gene encodes the enzyme tyrosinase, which is involved in the production of melanin from tyrosine. It has an allele, Ser192Tyr (rs1042602 ), found solely in 40–50% of Europeans and linked to light-colored skin in studies of South Asian and African-American populations. A number of genes known to affect skin color have alleles that show signs of positive selection in East Asian populations. Of these, only OCA2 has been directly related to skin color measurements, while DCT, MC1R and ATRN are marked as candidate genes for future study. Oculocutaneous albinism II (OCA2) assists in
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#17328916958531008-533: A range of populations. It has been the subject of recent selection in Western Eurasia, and is fixed in European populations. Solute carrier family 45 member 2 (SLC45A2 or MATP) aids in the transport and processing of tyrosine, a precursor to melanin. It has also been shown to be one of the significant components of the skin color of modern Europeans through its Phe374Leu ( rs16891982 ) allele that has been directly correlated with skin color variation across
1092-452: A result of genetics . The term "tanning" has a cultural origin, arising from the color tan. Its origin lies in the Western culture of Europe when it became fashionable for young women to seek a less pale complexion (see Cultural history below). Excessive exposure may in the long-term increase the risk of skin cancer , as well as depressed immune system function and accelerated aging of
1176-568: A result of tanning due to exposure to sunlight . The leading theory is that skin color adapts to intense sunlight irradiation to provide partial protection against the ultraviolet fraction that produces damage and thus mutations in the DNA of the skin cells. In some populations, women are significantly lighter-skinned than men . However, in other populations, notably those of European descent, men are significantly lighter-skinned than women. European women may have darker skin than European men due to
1260-462: A scientific expedition went to the island of Tenerife to test the wider health benefits of "heliotherapy", and by 1913 "sunbathing" was referred to as a desirable activity for the leisured class. Shortly thereafter, in the 1920s, fashion-designer Coco Chanel accidentally got sunburnt while visiting the French Riviera . When she arrived home, she arrived with a sun tan and her fans apparently liked
1344-680: A study addressing 40,000 years of modern human history, stated: "Relatively dark skin pigmentation in Early Upper Paleolithic Europe would be consistent with those populations being relatively poorly adapted to high-latitude conditions as a result of having recently migrated from lower latitudes. On the other hand, although we have shown that these populations carried few of the light pigmentation alleles that are segregating in present-day Europe, they may have carried different alleles that we cannot now detect." Solute carrier family 24 member 5 (SLC24A5) regulates calcium in melanocytes and
1428-433: A tanning effect without exposure to ultraviolet radiation, known as sunless tanning . Moderate exposure to direct sunlight contributes to the production of melanin and vitamin D by the body . Excessive exposure to ultraviolet rays has negative health effects, including sunburn . Some people tan or sunburn more easily than others. This may be the result of different skin types and natural skin color , and these may be
1512-509: A three-way model for the evolution of human skin color, with dark skin evolving in early Homo sapiens in Africa and light skin evolving only recently after modern humans had expanded out of Africa . For the most part, the evolution of light skin has followed different genetic paths in Western and Eastern Eurasian populations; however, some mutations associated with lighter skin have estimated origin dates after humans spread out of Africa but before
1596-431: Is sunburn , the speed and severity of which vary among individuals. This can be alleviated at least to some extent by the prior application of a suitable-strength sunscreen , which also hinders the tanning process due to the blocking of UV light. Overexposure to ultraviolet radiation is known to cause skin cancer , make skin age and wrinkle faster, mutate DNA , and impair the immune system. Frequent tanning bed use triples
1680-498: Is consistent with positive selection for the high-eumelanin phenotype seen in Africa and other environments with high UV exposure. For the most part, the evolution of light skin has followed different genetic paths in European and East Asian populations. Two genes, however, KITLG and ASIP , have mutations associated with lighter skin that have high frequencies in both European and East Asian populations. They are thought to have originated after humans spread out of Africa but before
1764-451: Is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis. The red color underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or sexual arousal , or the stimulation of the nervous system ( anger , embarrassment ), arterioles dilate. Color is not entirely uniform across an individual's skin; for example,
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#17328916958531848-551: Is due to the preservation of this ancestral state and not due to new variations on a previously lightened population. The melanocortin 1 receptor (MC1R) gene is primarily responsible for determining whether pheomelanin and eumelanin are produced in the human body. Research shows at least 10 differences in MC1R between African and chimpanzee samples and that the gene has probably undergone a strong positive selection (a selective sweep ) in early Hominins around 1.2 million years ago. This
1932-476: Is important in the process of melanogenesis . The SLC24A5 gene's derived Ala111Thr allele (rs1426654 ) has been shown to be a major factor in light skin pigmentation and is common in Western Eurasia . Recent studies have found that the variant represents as much as 25–40% of the average skin tone difference between Europeans and West Africans. This derived allele is a reliable predictor of phenotype across
2016-820: Is involved in the permanent survival, proliferation and migration of melanocytes. A mutation in this gene, A326G (rs642742 ), has been positively associated with variations of skin color in African-Americans of mixed West African and European descent and is estimated to account for 15–20% of the melanin difference between African and European populations. This allele shows signs of strong positive selection outside Africa and occurs in over 80% of European and Asian samples, compared with less than 10% in African samples. Agouti signalling peptide (ASIP) acts as an inverse agonist , binding in place of alpha-MSH and thus inhibiting eumelanin production. Studies have found two alleles in
2100-687: Is partially supported by a study into the SLC24A5 gene which found that the allele associated with light skin in Europe "determined […] that 18,000 years had passed since the light-skin allele was fixed in Europeans" but may have originated as recently as 12,000–6,000 years ago "given the imprecision of method" , which is in line with the earliest evidence of farming. Paleolithic Cro-Magnon groups, as well as Early Holocene Western and central European hunter-gatherers ( Western Hunter Gatherers ) have been suggested to have been dark skinned based on DNA analysis, with
2184-492: Is produced by cells called melanocytes in a process called melanogenesis . Melanin is made within small membrane–bound packages called melanosomes . As they become full of melanin, they move into the slender arms of melanocytes, from where they are transferred to the keratinocytes . Under normal conditions, melanosomes cover the upper part of the keratinocytes and protect them from genetic damage. One melanocyte supplies melanin to thirty-six keratinocytes according to signals from
2268-454: Is significantly associated with skin color variation in African-Americans and the ancestral version occurs in only 12% of European and 28% of East Asian samples compared with 80% of West African samples. A number of genes have been positively associated with the skin pigmentation difference between European and non-European populations. Mutations in SLC24A5 and SLC45A2 are believed to account for
2352-428: Is the pigmentation of interfollicular epidermis , because it improves barrier function as compared to non-pigmented skin. The authors argue that lack of significant differences between modern light-skinned and dark-skinned populations in vitamin D deficiency, early death from UV-induced cancers and birth defects — as well as instances of light and dark populations living side-by-side in areas with similar UV — suggest
2436-451: The Clark's level system, which uses the microscopic appearance of a melanoma to predict its clinical course and prognosis. Fitzpatrick's group also produced the first systematic study of the early warning signs of melanoma. He investigated the role of sunlight and especially sunburn in the development of melanoma. In 1975, he devised the Fitzpatrick scale of skin phototypes, which described
2520-918: The DSM-IV criteria for addiction. Several organizations, such as the World Health Organization (WHO), the American Cancer Society and the US Surgeon General have issued guidelines warning about sun tanning and UV radiation exposure, either from the sun or from indoor tanning . Production of vitamin D is essential for human health. Moderate exposure (avoiding sunburn) to UV radiation provides benefits such as increased vitamin D, as well as other possible benefits that are still being studied. Several tanning activators have used different forms of psoralen , which are known to be photocarcinogenic . Health authorities have banned psoralen since July 1996. In
2604-698: The Massachusetts General Hospital Dermatology Service from 1959 to 1987. He has been described as "the father of modern academic dermatology" and as "the most influential dermatologist of the last 100 years", in part because he trained so many of the leaders in the field. Fitzpatrick was born in Madison, Wisconsin , on December 19, 1919. He earned a bachelor's degree from the University of Wisconsin . He then received an M.D. degree from Harvard Medical School , where he became interested in
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2688-587: The University of Oregon . In 1959, still only 39, he was named chair of the Dermatology Department at Harvard Medical School, the youngest professor and chair at Harvard. He conducted early research on melanoma . In 1966 he and dermatopathologist Wallace H. Clark Jr. , together with John Raker and Martin C. Mihm Jr., created the first Pigmented Lesion Clinic in the United States at Massachusetts General Hospital. Clark's studies at that clinic resulted in
2772-869: The advent of farming and thus have taken place only around 6,000 years ago; This scenario found support in a 2014 analysis of mesolithic (7,000 years old) hunter-gatherer DNA from La Braña , Spain, which showed a version of these genes not corresponding with light skin color. In 2015, researchers analysed for light skin genes in the DNA of 94 ancient skeletons ranging from 8,000 to 3,000 years old from Europe and Russia. They found c. 8,000-year-old hunter-gatherers in Spain, Luxembourg, and Hungary were dark skinned while similarly aged hunter gatherers in Sweden were light skinned (having predominately derived alleles of SLC24A5, SLC45A2 and also HERC2/OCA2). Neolithic farmers entering Europe at around
2856-426: The lightest hues. Differences in skin color among individuals is caused by variation in pigmentation , which is the result of genetics (inherited from one's biological parents ), exposure to the sun , disorders, or some combination thereof. Differences across populations evolved through natural selection or sexual selection , because of social norms and differences in environment, as well as regulations of
2940-477: The scrotum in males. In some people, the armpits become slightly darker during puberty. The interaction of genetic, hormonal, and environmental factors on skin coloration with age is still not adequately understood, but it is known that men are at their darkest baseline skin color around the age of 30, without considering the effects of tanning. Around the same age, women experience darkening of some areas of their skin. Human skin color fades with age. Humans over
3024-400: The 1950s, baby oil was commonly used to increase tanning. Coppertone , in 1953, marketed its sunscreen with a drawing of a young girl and her cocker spaniel tugging on her bathing suit bottom, revealing her bare bottom and tan line; this advertisement was modified around the turn of the 21st century and now shows a little girl wearing a one-piece bathing suit or shorts. In the latter part of
3108-570: The 1950s, silver metallic reflectors were common to enhance one's tan. In 1962, sunscreen commenced to be SPF rated, although SPF labeling in the US was not standardized by the FDA until 1978. In the 1970s, Mattel introduced Malibu Barbie , which had tanned skin and further popularized sun tanning among women. In 1978, both sunscreen with an SPF 15 rating as well as tanning beds first appeared. In 2007, there were an estimated 50,000 outlets for indoor tanning; it
3192-503: The UVA and UVB ranges. Ultraviolet A (UVA) radiation is in the wavelength range 320 to 400 nm. Ultraviolet B (UVB) radiation is in the wavelength range 280 to 320 nm. Much of this band is blocked by the Earth's ozone layer, but some penetrates. UVB: A person's natural skin color affects their reaction to exposure to sunlight. An individual's natural skin color can vary from a dark brown to
3276-404: The United States and Western Europe before the 1920s, tanned skin was associated with the lower classes because they worked outdoors and were exposed to the sunlight. Parasols and long sleeves were typically worn, even at beaches. By the 1920s, however, a cultural transformation took place, and tan skin became the ideal. By the early 20th century, therapeutic benefits of sunlight were advertised to
3360-452: The age of thirty experience a decrease in melanin-producing cells by about 10% to 20% per decade as melanocyte stem cells gradually die. The skin of face and hands has about twice the amount of pigment cells as unexposed areas of the body, as chronic exposure to the sun continues to stimulate melanocytes. The blotchy appearance of skin color in the face and hands of older people is due to the uneven distribution of pigment cells and to changes in
3444-456: The allele for dark skin present in modern Africans arose at least by 1.2 million years ago. This was the genotype inherited by anatomically modern humans , but retained only by part of the extant populations, thus forming an aspect of human genetic variation . About 100,000–70,000 years ago, some anatomically modern humans ( Homo sapiens ) began to migrate away from the tropics to the north where they were exposed to less intense sunlight. This
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3528-451: The amount of ultraviolet (UV) radiation from the sun that penetrates the skin by absorption. While UV radiation can assist in the production of vitamin D, excessive exposure to UV can damage health. Loss of body hair in Homo links to the thermoregulation through perspiration heat dissipation required for activity in hot open environments and endurance running . Humans as primates have
3612-490: The beach in order to protect the wearer's face from the effects of sunlight. A 1969 innovation is tan-through swimwear , which uses fabric perforated with thousands of micro holes that are nearly invisible to the naked eye, but which transmit enough sunlight to approach an all-over tan, especially if the fabric is stretched taut. Tan-through swimwear typically allows more than one-third of UV rays to pass through (equivalent to SPF 3 or less), and an application of sunscreen even to
3696-401: The biochemical effects of ultraviolet radiation penetrating the skin. The actual skin color of different humans is affected by many substances, although the single most important substance is the pigment melanin . Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skin humans. The skin color of people with light skin
3780-531: The bulk of this variation and show very strong signs of selection. A variation in TYR has also been identified as a contributor. Research indicates the selection for the light-skin alleles of these genes in Europeans is comparatively recent, having occurred later than 20,000 years ago and perhaps as recently as 12,000 to 6,000 years ago. In the 1970s, Luca Cavalli-Sforza suggested that the selective sweep that rendered light skin ubiquitous in Europe might be correlated with
3864-428: The common tanning behaviour of various skin types. He worked with other researchers and with industry to develop and test some of the first modern sunscreens . He was a developer of PUVA therapy for the treatment of psoriasis and other skin disorders. Basic science discoveries included the discovery of the melanosome and of human tyrosinase . He created and edited the first major clinical reference book in
3948-454: The covered area is recommended. To avoid exposure to UVB and UVA rays, or in seasons without strong sunshine, some people take alternative steps to appear with darkened skin. They may use sunless tanning (also known as self-tanners); stainers that are based on dihydroxyacetone (DHA); or cosmetics such as bronzers. Many sunless tanning products are available in the form of darkening creams, gels , lotions , and sprays that are self-applied on
4032-474: The damage and protect the skin by creating and releasing further melanin into the skin's cells. With the production of the melanin, the skin color darkens. The tanning process can be triggered by natural sunlight or by artificial UV radiation, which can be delivered in frequencies of UVA, UVB, or a combination of both. The intensity is commonly measured by the UV Index . There are two different mechanisms involved in
4116-520: The dimorphism. Breastfeeding newborns, whose skeletons are growing, require high amounts of calcium intake from the mother's milk (about 4 times more than during prenatal development), part of which comes from reserves in the mother's skeleton. Thomas B. Fitzpatrick Thomas B. Fitzpatrick (December 19, 1919 – November 16, 2003) was an American dermatologist . He was Chairman of the Department of Dermatology at Harvard Medical School and Chief of
4200-515: The divergence of West Eurasians and East Asians. Elias et. al. in 2010 showed a superior barrier function in darkly pigmented skin. Most protective functions of the skin, including the permeability barrier and the antimicrobial barrier, reside in the stratum corneum and the researchers surmise that the stratum corneum has undergone the most genetic change since the loss of human body hair. Natural selection would have favored mutations that protect this essential barrier; one such protective adaptation
4284-426: The divergence of the European and Asian lineages around 30,000 years ago. Two subsequent genome-wide association studies found no significant correlation between these genes and skin color, and suggest that the earlier findings may have been the result of incorrect correction methods and small panel sizes, or that the genes have an effect too small to be detected by the larger studies. The KIT ligand (KITLG) gene
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#17328916958534368-411: The divergence of the two lineages. According to Crawford et al. (2017), most of the genetic variants associated with light and dark pigmentation in African populations appear to have originated more than 300,000 years ago. African, South Asian and Australo-Melanesian populations also carry derived alleles for dark skin pigmentation that are not found in Europeans or East Asians. Huang et al. 2021 found
4452-445: The evolution of hairless skin, abundant sweat glands, and skin rich in melanin, early humans could walk, run, and forage for food for long periods of time under the hot sun without brain damage due to overheating, giving them an evolutionary advantage over other species. Research on the MC1R alleles using assumptions about past population size and an absence of population bottlenecks suggests
4536-557: The evolution of human skin color, see section above. For skin color, heritability is very high, even though it can be modified by exposure to sunlight. A recent systematic study found 169 genes involved in human skin coloration. Most of the genes were involved in melanosome biogenesis, endosomal transport, and gene regulation . Notably, the function of these genes was verified in tissue culture experiments using CRISPR-Cas9 knockouts, showing that these genes are indeed involved in melanin production. All modern humans share
4620-463: The evolution of light skin in East Asian populations. Tanning response in humans is controlled by a variety of genes. MC1R variants Arg151Sys (rs1805007 ), Arg160Trp (rs1805008 ), Asp294Sys (rs1805009 ), Val60Leu (rs1805005 ) and Val92Met (rs2228479 ) have been associated with reduced tanning response in European and/or East Asian populations. These alleles show no signs of positive selection and only occur in relatively small numbers, reaching
4704-409: The existence of "selective pressure on light pigmentation in the ancestral population of Europeans and East Asians", prior to their divergence from each other. Skin pigmentation was also found to be affected by directional selection towards darker skin among Africans, as well as lighter skin among Eurasians. Crawford et al. (2017) similarly found evidence for selection towards light pigmentation prior to
4788-436: The female sex hormone estrogen is known to increase skin pigmentation in lighter-skinned populations. White women's skin is significantly darker than White men's, to the extent that White women have a much lower rate of skin cancer than White men. In populations where women have lighter skin than men, it has been hypothesized that the requirement for high amounts of calcium during pregnancy and lactation may be related to
4872-416: The female sex hormone estrogen , which darkens light skin. Women from darker-skinned populations may have evolved to lighter skin than men so their bodies could absorb more vitamin D during pregnancy, which improves calcium absorption. The social significance of differences in skin color has varied across cultures and over time, as demonstrated with regard to social status and discrimination . Melanin
4956-412: The increased exposure to sunlight. In 2017, a study showed that both dark and light pigmentation alleles arose before the origin of modern humans, with the older version of the variants in many cases being associated with lighter skin. The earliest primate ancestors of humans most likely had pale non-pigmented skin covered with dark black hair, like the chimpanzee and other great apes. With
5040-424: The interaction between melanocytes and keratinocytes . It has been observed that females are found to have lighter skin pigmentation than males in some studied populations. However, in light skinned populations, namely those of European descent, women have darker skin than men. It is unknown why skin color is sexually dimorphic in some populations. White women may have darker skin than white men because
5124-467: The keratinocytes. They also regulate melanin production and replication of melanocytes. People have different skin colors mainly because their melanocytes produce different amount and kinds of melanin. The genetic mechanism behind human skin color is mainly regulated by the enzyme tyrosinase , which creates the color of the skin, eyes, and hair shades. Differences in skin color are also attributed to differences in size and distribution of melanosomes in
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#17328916958535208-538: The look and started to adopt darker skin tones themselves. Tanned skin became a trend partly because of Coco's status and the longing for her lifestyle by other members of society. In addition, Parisians fell in love with Josephine Baker , a "caramel-skinned" singer in Paris , and idolized her darker skin. These two women were leading figures of the transformation that tan skin underwent, in which it became perceived as fashionable, healthy, and luxurious. Jean Patou capitalized on
5292-609: The lowest frequencies in Western China and some Eastern European populations. A number of studies have found genes linked to human skin pigmentation that have alleles with statistically significant frequencies in Chinese and East Asian populations. While not linked to measurements of skin tone variation directly, dopachrome tautomerase (DCT or TYRP2 rs2031526 ), melanocortin 1 receptor (MC1R) Arg163Gln (rs885479 ) and attractin (ATRN ) have been indicated as potential contributors to
5376-463: The new tanning fad, launching the first sun tan oil "Huile de Chaldee" in 1927. Just before the 1930s, sunlight therapy became a popularly subscribed cure for almost every ailment from simple fatigue to tuberculosis. In the 1940s, advertisements encouraging sunbathing began to appear in women's magazines. At the same time, swimsuits ' skin coverage began decreasing, with the bikini radically changing swimsuit style after it made its appearance in 1946. In
5460-443: The production of a tan by UV exposure: Firstly, UVA radiation creates oxidative stress, which in turn oxidizes existing melanin and leads to rapid darkening of the melanin. UVA may also cause melanin to be redistributed (released from melanocytes where it is already stored), but its total quantity is unchanged. Skin darkening from UVA exposure does not lead to significantly increased production of melanin or protection against sunburn. In
5544-522: The public. In 1903, Niels Finsen was awarded the Nobel Prize in Medicine for his "Finsen Light Therapy". The therapy was a cure for diseases such as lupus vulgaris and rickets . Vitamin D deficiency was found to be a cause of rickets, and exposure to sunlight would allow vitamin D to be produced in a person. Therefore, sunlight exposure was a remedy to curing several diseases, especially rickets. In 1910
5628-613: The regulation of pH in melanocytes. The OCA2 gene's derived His615Arg (rs1800414 ) allele has been shown to account for about 8% of the skin tone difference between African and East Asian populations in studies of an East Asian population living in Toronto and a Chinese Han population. This variant is essentially restricted to East Asia, with highest frequencies in Eastern East Asia (49–63%), midrange frequencies in Southeast Asia, and
5712-518: The relatively new specialty of dermatology. After an internship at Boston City Hospital he went to the University of Minnesota for a Ph.D. in pathology. After two years at the Army Medical Center during World War II, he trained in clinical dermatology at the University of Michigan and the Mayo Clinic . At the age of 32, fresh out of training, he became Professor and Chair of Dermatology at
5796-561: The risk of developing melanoma , the deadliest form of skin cancer, according to a 2010 study. The study suggests that the melanoma risk is linked more closely to total exposure than it is to the age at which an individual first uses a tanning bed. Frequent tanning also has behavioural reinforcing effects, following UVA radiation epidermal keratinocytes synthesize POMC inducing the production of β - Endorphins , which are opioid agonists. An opioid blockade also then causes withdrawal signs after habitual UV exposure leading to many tanners meeting
5880-463: The same time were intermediate, being nearly fixed for the derived SLC24A5 variant but only having the derived SLC45A2 allele in low frequencies. The SLC24A5 variant spread very rapidly throughout central and southern Europe from about 8,000 years ago, whereas the light skin variant of SLC45A2 spread throughout Europe after 5,800 years ago. Some authors have expressed caution regarding the skin pigmentation predictions. According to Ju et al. (2021), in
5964-434: The second process, triggered primarily by UVB, there is an increase in production of melanin (melanogenesis), which is the body's reaction to direct DNA photodamage (formation of pyrimidine dimers ) from UV radiation. Melanogenesis leads to delayed tanning, and typically becomes visible two or three days after exposure. The tan that is created by increased melanogenesis typically lasts for a few weeks or months, much longer than
6048-432: The skin . Melanin is a natural pigment produced by cells called melanocytes in a process called melanogenesis . Melanocytes produce two types of melanin: pheomelanin (red) and eumelanin (very dark brown). Melanin protects the body by absorbing ultraviolet radiation. Excessive UV radiation causes sunburn along with other direct and indirect DNA damage to the skin, and the body naturally combats and seeks to repair
6132-424: The skin is exposed to more sun. All human babies are born pale, regardless of what their adult color will be. In humans, melanin production does not peak until after puberty. The skin of children becomes darker as they go through puberty and experience the effects of sex hormones. This darkening is especially noticeable in the skin of the nipples , the areola of the nipples, the labia majora in females, and
6216-447: The skin of the palm and the sole is lighter than most other skin, and this is especially noticeable in darker-skinned people. There is a direct correlation between the geographic distribution of ultraviolet radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Areas that receive higher amounts of UVR, generally located closer to the equator, tend to have darker-skinned populations. Areas that are far from
6300-423: The skin. Melanocytes produce two types of melanin. The most common form of biological melanin is eumelanin , a brown-black polymer of dihydroxyindole carboxylic acids , and their reduced forms. Most are derived from the amino acid tyrosine . Eumelanin is found in hair, areola , and skin, and the hair colors gray, black, blond, and brown. In humans, it is more abundant in people with dark skin. Pheomelanin ,
6384-421: The skin. There is also a professional spray-on tanning option or " tanning booth " that is offered by spas , salons , and tanning businesses. Spray tanning does not involve a color being sprayed on the body, instead it uses a colorless chemical that reacts with proteins in the top layer of the skin, resulting in a brown color. Human skin color Human skin color ranges from the darkest brown to
6468-454: The standard model is insufficient to explain the strong selection drive for pigmented skin. Jablonski rejects this theory on the grounds that the human tanning response is driven by UV-B exposure, not xeric stress, and that the positive selection for vitamin D production is "well-established". To some extent, skin color is determined independently of eye and hair color, as can be seen from variation in skin coloration in human populations. For
6552-656: The tan that is caused by oxidation of existing melanin, and is also actually protective against UV skin damage and sunburn, rather than simply cosmetic. Typically, it can provide a modest Sun Protection Factor (SPF) of 3, meaning that tanned skin would tolerate up to 3 times the UV exposure as pale skin. However, in order to cause true melanogenesis-tanning by means of UV exposure, some direct DNA photodamage must first be produced, and this requires UVB exposure (as present in natural sunlight, or sunlamps that produce UVB). The ultraviolet frequencies responsible for tanning are often divided into
6636-550: The tropics and closer to the poles have lower intensity of UVR, which is reflected in lighter-skinned populations. By the time modern Homo sapiens evolved, all humans were dark-skinned. Some researchers suggest that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa as they migrated to different UV zones, and that such major changes in pigmentation may have happened in as little as 100 generations (≈2,500 years) through selective sweeps . Natural skin color can also darken as
6720-412: The vicinity of ASIP are associated with skin color variation in humans. One, rs2424984, has been identified as an indicator of skin reflectance in a forensics analysis of human phenotypes across Caucasian, African-American, South Asian, East Asian, Hispanic and Native American populations and is about three times more common in non-African populations than in Africa. The other allele, 8188G (rs6058017 )
6804-449: Was a five-billion-dollar industry in the United States, and had spawned an auxiliary industry for indoor tanning lotions including bronzers, intensifiers, and accelerators. Since then, the indoor tanning industry has become more constrained by health regulations. In China, darker skin is still considered by many to be the mark of the lower classes. As recently as 2012, in some parts of China, ski masks were becoming popular items to wear at
6888-441: Was a strong evolutionary pressure which acted on the development of dark skin pigmentation in early members of the genus Homo . Hairlessness exposes folate circulating subcutaneously and in the dermis to degradation from UV-radiation . The effect of sunlight on folic acid levels has been crucial in the development of dark skin and favored the emergence of skin pigmentation in order to protect from folate depletion due to
6972-482: Was exposed to sunlight. In the tropics, natural selection favoured dark-skinned human populations as high levels of skin pigmentation protected against the harmful effects of sunlight. Indigenous populations' skin reflectance (the amount of sunlight the skin reflects) and the actual UV radiation in a particular geographic area is highly correlated, which supports this idea. Genetic evidence also supports this notion, demonstrating that around 1.2 million years ago there
7056-404: Was possibly in part due to the need for greater use of clothing to protect against the colder climate. Under these conditions there was less photodestruction of folate and so the evolutionary pressure working against the survival of lighter-skinned gene variants was reduced. In addition, lighter skin is able to generate more vitamin D (cholecalciferol) than darker skin, so it would have represented
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