sun tanning sun tanning 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 which can produce a tanning effect without exposure to ultraviolet radiation, known as sunless tanning. a visible tan line on a woman whose skin has been darkened by ultraviolet exposure, except where covered. impact on skin health moderate exposure a sun tanned arm showing browner skin where it has been exposed moderate exposure to direct sunlight contributes to the production of melanin and vitamin d by the body excessive exposure 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 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). long-term photoaging of a woman. excessive exposure may in the long-term increase the risk of skin cancer, as well as depressed immune system function and accelerated aging of the skin. tanning process 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 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. cross-sectional view showing skin tone becoming darker due to the production of more melanin to overcome dna damage caused by uv radiation there are two different mechanisms involved in 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 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). the ultraviolet frequencies responsible for tanning are often divided into the uva and uvb ranges. uva ultraviolet a (uva) radiation is in the wavelength range 320 to 400 nm. it is present more uniformly throughout the day, and throughout the year, than uvb. most uva is not blocked by the atmosphere's ozone layer. uva causes the release of existing melanin from the melanocytes to combine with oxygen (oxidize) to create the actual tan color in the skin. uva is blocked less than uvb by many sunscreens, but is blocked to some degree by clothing. uva is known both to cause dna damage and to be carcinogenic. however, it operates not by inducing direct dna damage, but by producing reactive oxygen species which damage dna indirectly. uva (see above) induces a cosmetic tan but little extra melanin protection against sun damage, sun burn, or cancer. uvb 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: triggers the formation of cpd-dna damage (direct dna damage), which in turn induces an increased melanin production. is more likely to cause a sunburn than uva as a result of overexposure. the mechanism for sunburn and increased melanogenesis is identical. both are caused by the direct dna damage (formation of cpds). produces vitamin d in human skin. is reduced by virtually all sunscreens in accordance with their spf. is thought, but not proven, to cause the formation of moles and some types of skin cancer. causes skin aging (but at a slower rate than uva). stimulates the production of new melanin, which leads to an increase in the dark-colored pigment within a few days. tanning behavior of different skin colors 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 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: typealso calledsunburningtanning behaviorvon luschan scale ivery light or paleoftenoccasionally1–5 iilight or light-skinnedusuallysometimes6–10 iiilight intermediaterarelyusually11–15 ivdark intermediaterarelyoften16–21 vdark or "brown" typenosometimes darkens22–28 vivery dark or "black" typenonaturally black-brown skin29–36 health aspects main article: health effects of sunlight exposure sunburn peeling disappearing sun tan, revealing the individual's naturally light-colored skin. 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. 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 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. the international agency for research on cancer places the use of tanning beds in the highest cancer risk category, describing them as carcinogenic to humans even if used as recommended. 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 will also then cause withdrawal signs after habitual uv exposure leading to many tanners meeting 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. cultural history