Sun tanning or simply tanning is the process whereby skin color is darkened or tanned. It is most often a result of exposure to ultraviolet (UV) radiation from the sun or from artificial sources, such as a tanning bed. People who deliberately tan their skin by exposure to the sun engage in sun bathing. Some people use chemical products which can produce a tanning effect without exposure to ultraviolet radiation.
Moderate exposure to the sun contributes to the production of 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 ageing 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.
Several cases of tanning addiction have been reported. Though the mechanism by which tanning addiction occurs is unknown, some evidence indicates that the release of endorphins during the tanning process causes the pleasurable effects that underlie the addiction.
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).
Melanin is 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 solar radiation. Excessive solar radiation causes 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, but the UV-B in sunlight can also cause sunburn. The tanning process can also be created by artificial UV radiation, which can be delivered in frequencies of UV-A, UV-B, or a combination of both.
There are two different mechanisms involved in production of a tan by UV exposure: Firstly, UV-A radiation creates oxidative stress, which in turn oxidises existing melanin and leads to rapid darkening of the melanin. UV-A may also cause melanin to be redistributed (released from melanocytes where it is already stored), but its total quantity is unchanged. Thus, the effect of UV-A leads to skin darkening, but this is only cosmetic since it does not lead to greatly increased production of melanin and therefore also to little increase in protection against UV-B, or protection against sunburn.
In the second process, triggered primarily by UV-B, there is an increase in production of melanin (melanogenesis), which is the body's reaction to direct photodamage (formation of pyrimidine dimers) from UV radiation. 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, and is also actually protective against UV skin damage and sunburn, rather than simply cosmetic. However, in order to cause true melanogenesis-tanning by means of UV exposure, some direct DNA photodamage must first be produced, and this requires UV-B exposure (as present in natural sunlight, or sunlamps that produce UV-B).
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 UV-B. UV-A is not blocked by the ozone layer. UV-A causes the release of existing melanin from the melanocytes to combine with oxygen (oxidize) to create the actual tan color in the skin. It is blocked less than UV-B by many sunscreens, but is blocked to some degree by clothing. UV-A 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. UV-A (see above) apparently induces a cosmetic tan but little extra melanin protection against sun damage, sun burn, or cancer.
Ultraviolet B (UV-B or 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. UV-B does the following:
- 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
- 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 far slower rate than UVA.)
- stimulates the production of new melanin, which leads to an increase in the dark-coloured pigment within a few days.
Tanning behavior of different skin colors
A person's natural skin color has an impact on 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 reddish due to the blood in the skin. In 1975, Harvard dermatologist Thomas B. Fitzpatrick devised the Fitzpatrick scale which described the common tanning behavior of various skin types, as follows: 
|Type||Also called||Sunburning||Tanning behavior||von Luschan scale|
|I||Very light or pale||Often||Occasionally||1–5|
|II||Light or light-skinned||Usually||Sometimes||6–10|
|V||Dark or "brown" type||No||Sometimes darkens||22–28|
|VI||Very dark or "black" type||No||Naturally black-brown skin||29–36|
To avoid exposure to UVB and UVA rays, or in sunless seasons, some people take steps to appear with darkened skin. They may use sunless tanning (also known as self-tanners); stainers which are based on dihydroxyacetone (DHA); bronzers, which are simply dyes; tan accelerators, based on tyrosine and psoralens. Some people use make-up to create a tanned appearance while others may get a tanned appearance by wearing tan colored stockings or pantyhose.
Many sunless tanning products are available in the form of creams, gels, lotions, and sprays that are self-applied on the skin. Another option is the use of bronzers which are cosmetics that provide temporary effects. There is also a professional spray-on tanning option or “tanning booths” that is offered by spas, salons, and tanning businesses.
Spray tanning does not mean that a color is sprayed on the body. What is used in the spray tanning process is a colorless chemical which reacts with proteins in the top layer of the skin, resulting in a brown color. The two main active ingredients used in most of the sunless tanners are dihydroxyacetone and erythrulose.
The U.S. Food and Drug Administration (FDA) has not approved the use of DHA spray tanning booths because it has not received safety data to support this specific use. DHA is a permitted color additive for cosmetic use restricted to external application. When used in a commercial spray tanning booth, areas such as the eyes, lips or mucous membrane are exposed to the DHA which is a non-permitted use of the product.
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. The International Agency for Research on Cancer places the use of tanning beds at the highest cancer risk category, describing them as carcinogenic to humans, if used as the manufacturer recommends. Tanning bed use under the age of 35 increases melanoma risk by 87%. In Australia, 1 in 6 melanomas in people aged 18 to 29 are caused by tanning beds, and they have been attributed to an estimated 281 new melanomas a year, 43 melanoma-related deaths, and 2,572 new cases of squamous cell carcinoma.
Throughout history, tanning has gone in and out of fashion. In United States before about the 1920s, tanned skin was associated with the lower classes, because they worked outdoors and were exposed to the sun. Women went to great lengths to preserve pallid skin, as a sign of their "refinement".
Women's outdoor clothing styles were tailored to protect against sun exposure, with full length sleeves, and sunbonnets and other large hats, headscarves, and parasols shielding the head. Women even went as far as to put lead-based cosmetics on their skin to artificially whiten their skin tone. However, when not strictly monitored these cosmetics caused lead poisoning. Light-skinned appearance was achieved in other ways, including the use of arsenic to whiten skin, and lightening powders. The preference for fair-skin continued until the end of the Victorian era.
By the early 20th century the therapeutic benefits of sunlight began to be recognised. 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 disease, and exposure to the sun would allow vitamin D to be produced in a person. Therefore, sun exposure was a remedy to curing several diseases, especially rickets. In 1910 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 suntan and her fans apparently liked 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 idolised her dark skin. These two women were leading figures of the transformation tanned skin underwent, in which it became perceived as fashionable, healthy, and luxurious. Jean Patou capitalised on the new tanning fad launching the first suntan oil "Huile de Chaldee" in 1927.
Just before the 1930s sun therapy became a very popular subscribed cure for almost everything from simple fatigue to tuberculosis. In the 1940s, advertisements started appearing in women’s magazines which encouraged sun bathing. At the same time, swimsuits' skin coverage began decreasing, with the bikini radically changing swimsuit style after it made its appearance in 1946. In the 1950s, many people used baby oil as a method to increase tanning. The first self-tanner came about in the same decade and was known as “Man-Tan,” although it often led to undesirable orange skin. Coppertone, in 1953, marketed their sunscreen by placing a little blond girl and her cocker spaniel tugging on her bathing suit bottoms on the cover of their bottles; this is still the same advertisement used today. In the latter part of the 1950s, silver metallic UV reflectors were common to enhance one’s tan.
In 1962, sunscreen commenced to be SPF rated, although in the US SPF labeling was not standardised by the FDA until 1978. In 1971, Mattel introduced Malibu Barbie, which had tanned skin, sunglasses, and her very own bottle of sun tanning lotion. In 1978, both sunscreen with an SPF 15 rating as well as tanning beds first appeared. Today there are an estimated 50,000 outlets for tanning, whereas in the 1990s there were only around 10,000. The tanning business is a five-billion dollar industry in the United States. 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 the beach in order to protect the wearer's face from the effects of the sun.
Visible tan lines are regarded by many people to be un-aesthetic and embarrassing. Many people desire to avoid creation of tan lines on those parts of the body which will be visible when they are fully clothed. Some people try to achieve an all-over tan or to maximize their tan coverage. To achieve an all-over tan, the tanner needs to dispense with clothing; and to maximize covering, they need to minimize the amount of clothing they wear while tanning. For those women who cannot dispense with a swimsuit, they at times tan with the back strap undone while lying on the front, or removing shoulder straps, besides wearing swimsuits which cover less area than their normal clothing. Any exposure is subject to local community standards and personal choice. Some people tan in the privacy of their backyard where they can at times tan without clothes, and some countries have set aside clothing-optional swimming areas (also known as nude beaches), where people can tan and swim clothes-free. Some people tan topless, and others wear very brief swimwear, such as a microkini. A 1969 innovation of tan-through swimwear uses fabric which is perforated with thousands of micro holes that are nearly invisible to the naked eye, but which let enough sunlight through to produce a line-free tan. Tan-through swimsuits offer SPF protection of about 6, and an application of full-strength sunscreen even to the covered area is recommended.
- Sunless tanning
- Tanning booth
- Tanning bed
- Health effects of sun exposure
- Skin whitening
- Sun glasses
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|Wikimedia Commons has media related to Sunbathing.|
- Aim at Melanoma
- Information on tanning from The Skin Cancer Foundation
- Research on the benefits of UV exposure