question: How come fair skinned people have harder time getting a tan? Can they even get a tan?
comment: A tan is basicaly the skin's response to damage done by the sun, by increasing melanin. Since lighter skinned people naturaly have less melanin, it is harder for them to produce more. They can get a tan, but that tan will be lighter than a naturaly darker person's tan. It is also not a good idea to try and "force" a tan, since the chances of getting sunburnt (and possibly worse) are high
passages: 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 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 a "fair/medium/olive" context.
   Whilst not all of these genes directly affect melanin production, most of them code for proteins that may play a significant role in melanogenesis and control melanin concentration. Some of these genes are found to be more prevalent in certain population than others.
  
  Section::::Health implications.
  
  Skin pigmentation is an evolutionary adaptation to the various UV radiation levels around the world. There are health implications of light-skinned people living in environments of high UV radiation. Various cultural practices increase problems related to health conditions of light skin, for example sunbathing among the light-skinned.
   Moderate exposure to direct sunlight contributes to the production of melanin and vitamin D by the body, but excessive exposure to ultraviolet rays has negative health effects, including sunburn and increased risk of skin cancer, as well as depressed immune system function and accelerated aging of the skin. 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 a result of genetics. 
   Modern lifestyles and mobility have created mismatch between skin color and environment for many individuals. Vitamin D deficiencies and UVR overexposure are concerns for many. It is important for these people individually to adjust their diet and lifestyle according to their skin color, the environment they live in, and the time of year. For practical purposes, such as exposure time for sun tanning, six skin types are distinguished following Fitzpatrick (1975), listed in order of decreasing lightness:
  
  Section::::Exposure to sun.:Fitzpatrick scale.
   A person's natural skin color affects their reaction to exposure to the sun. Generally, those who start out with darker skin color and more melanin have better abilities to tan. Individuals with very light skin and albinos have no ability to tan. The biggest differences resulting from sun exposure are visible in individuals who start out with moderately pigmented brown skin: the change is dramatically visible as tan lines, where parts of the skin which tanned are delineated from unexposed skin.
   In 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 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). 
   People with moderately pigmented skin (Types III-IV) are able to produce melanin in their skin in response to UVR. Normal tanning is usually delayed as it takes time for the melanins to move up in the epidermis. Heavy tanning does not approach the photoprotective effect against UVR-induced DNA damage compared to naturally occurring dark skin, however it offers great protection against seasonal variations in UVR. Gradually developed tan in the spring prevents sunburns in the summer. This mechanism is almost certainly the evolutionary reason behind the development of tanning behaviour.
   BULLET::::- causes skin aging (but at a slower rate than UVA).
  
  BULLET::::- stimulates the production of new melanin, which leads to an increase in the dark-colored pigment within a few days.
  
  Section::::Tanning behavior of different skin colors.
  
  A person's natural skin color affects their reaction to exposure to the sun. An individual's natural skin color can vary from a dark brown to a nearly colorless pigmentation, which may appear white. In 1975, Harvard dermatologist Thomas B. Fitzpatrick devised the Fitzpatrick scale which described the common tanning behavior of various skin types, as follows:
  
  Section::::Health aspects.
   Section::::Human adaptation.:Evolutionary origins.
   Although pseudoporphyria has no predilection toward any one race, it has been shown that fair-skinned children who are highly prone to sunburn are more likely to develop naproxen-induced pseudoporphyria than those children with skin types III or higher. Wallace et al. demonstrated that even in the absence of a history of blistering, children with light skin and blue or green eyes are at an increased risk of developing shallow scars on the face while taking naproxen.
  
  Section::::Causes.
   Section::::Africa.
  
  In many parts of Africa, women with lighter skin are thought to be more beautiful and likely to find more success than women of darker skin tones. Often this barrier leads to women turning to skin lightening treatments, many of which are harmful to the body.
  
  Historically, the cause of skin lightening goes back to colonialism, where individuals with lighter skin received greater privilege than those of darker tones. This built a racial hierarchy and color ranking within colonized African nations, leaving psychological effects on many of the darker skinned individuals.
   BULLET::::- Type III: White skin, may burn but tans easily
  
  BULLET::::- Type IV: Light brown/olive skin, hardly burns, tans easily
  
  BULLET::::- Type V: Brown skin, usually does not burn, tans easily
  
  BULLET::::- Type VI: Black skin, very unlikely to burn, becomes darker with UV radiation exposure
  
  Age also affects how skin reacts to sun. Children younger than six and adults older than sixty are more sensitive to sunlight.
   A number of rare mutations, which often run in families, greatly increase melanoma susceptibility. Several genes increase risks. Some rare genes have a relatively high risk of causing melanoma; some more common genes, such as a gene called MC1R that causes red hair, have a relatively lower elevated risk. Genetic testing can be used to search for the mutations.
   Melanin is a pigment in the epidermis that functions to protect keratinocytes from the damage caused by UV radiation; it is found in higher concentration 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), and AKs are uncommon in dark-skinned people of African descent. Other phenotypic features seen in fair-skinned individuals that are associated with an increased propensity to develop AKs include:
  
  BULLET::::- Freckling
  
  BULLET::::- Light hair and eye color
   Section::::Genetics.
   In people with naturally occurring dark skin, the tanning occurs with the dramatic mobilization of melanin upward in the epidermis and continues with the increased production of melanin. This accounts for the fact that dark-skinned people get visibly darker after one or two weeks of sun exposure, and then lose their colour after months when they stay out of the sun. Darkly pigmented people tend to exhibit fewer signs of aging in their skin than the lightly pigmented because their dark skin protects them from most photoaging.
   Light-skinned people living in high sunlight environments are more susceptible to the harmful UV rays of sunlight because of the lack of melanin produced in the skin. The most common risk that comes with high exposure to sunlight is the increased risk of sunburns. This increased risk has come along with the cultural practice of sunbathing, which is popular among some human populations. This cultural practice to gain tanned skin if not regulated properly can lead to sunburn, especially among very lightly-skinned humans. The overexposure to sunlight also can lead to basal cell carcinoma, which is a common form of skin cancer.
   Other mutations confer lower risk, but are more common in the population. People with mutations in the MC1R gene are two to four times more likely to develop melanoma than those with two wild-type (typical unaffected type) copies. MC1R mutations are very common; and all red-haired people have a mutated copy. Mutation of the MDM2 SNP309 gene is associated with increased risks for younger women.
  
  Fair- and red-haired people, persons with multiple atypical nevi or dysplastic nevi and persons born with giant congenital melanocytic nevi are at increased risk.
   Melanoma is the most deadly skin cancer, although it is easily cured in the early stages. The normal likelihood of developing melanoma depends on race, the number of moles the person has, family history, age, sex, and how much the person has been exposed to UV radiation. "BRCA2" mutation carriers have approximately double or triple the risk that they would normally have, including a higher than average risk of melanoma of the eye.
   Humans with light skin pigmentation have skin with low amounts of eumelanin, and possess fewer melanosomes than humans with dark skin pigmentation. Light skin provides better absorption qualities of ultraviolet radiation. This helps the body to synthesize higher amounts of vitamin D for bodily processes such as calcium development. Light-skinned people who live near the equator with high sunlight are at an increased risk of folate depletion. As consequence of folate depletion, they are at a higher risk of DNA damage, birth defects, and numerous types of cancers, especially skin cancer.
   The complete set of observable traits of the structure and behavior of an organism is called its phenotype. These traits arise from the interaction of its genotype with the environment. As a result, many aspects of an organism's phenotype are not inherited. For example, suntanned skin comes from the interaction between a person's phenotype and sunlight; thus, suntans are not passed on to people's children. However, some people tan more easily than others, due to differences in their genotype: a striking example is people with the inherited trait of albinism, who do not tan at all and are very sensitive to sunburn.
   A family history of melanoma greatly increases a person's risk because mutations in several genes have been found in melanoma-prone families. People with a history of one melanoma are at increased risk of developing a second primary tumor.
  
  Fair skin is the result of having less melanin in the skin, which means there is less protection from UV radiation. A family history could indicate a genetic predisposition to melanoma.
  
  Section::::Pathophysiology.
   The most common risk of exposure to ultraviolet radiation 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 will also hinder the tanning process due to the blocking of UV light.
   There are two different mechanisms involved in 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.
   There are two different mechanisms involved. Firstly, the UVA-radiation creates oxidative stress, which in turn oxidizes existing melanin and leads to rapid darkening of the melanin, also known as IPD (immediate pigment darkening). Secondly, there is an increase in production of melanin known as melanogenesis. Melanogenesis leads to delayed tanning and first becomes visible about 72 hours after exposure. The tan that is created by an increased melanogenesis lasts much longer than the one that is caused by oxidation of existing melanin. Tanning involves not just the increased melanin production in response to UV radiation but the thickening of the top layer of the epidermis, the stratum corneum.
  