Sunless tanning (also known as UV-free tanning, self tanning, spray tanning (when applied topically), or fake tanning) refers to the application of chemicals to the skin to produce an effect similar in appearance to a suntan. The popularity of sunless tanning has risen since the 1960s after links were made by health authorities between exposure to the sun and other sun tanning methods, such as sunbeds or tanning beds, and the incidence of skin cancer.
Artificial sunscreen absorbs ultraviolet light and prevents it from reaching the skin. It has been reported that sunscreen with a sun protection factor (SPF) of 8 based on the UVB spectrum can decrease vitamin D synthetic capacity by 95 percent, whereas sunscreen with an SPF of 15 can reduce synthetic capacity by 98 percent.
A safe and effective method of sunless tanning is consumption of certain carotenoids — antioxidants found in some fruits and vegetables such as carrots and tomatoes — which can result in changes to skin color when ingested chronically and/or in high amounts. Carotenoids are long-lasting. In addition, carotenoids have been linked to more attractive skin tone than suntan. Carotenes also fulfil the function of melanin in absorbing the UV radiation and protecting the skin. For example, they are concentrated in the macula of the eye to protect the retina from damage. They are used in plants both to protect chlorophyll from light damage and harvest light directly.
Carotenaemia (xanthaemia) is the presence in blood of the yellow pigment carotene from excessive intake of carrots or other vegetables containing the pigment resulting in increased serum carotenoids. It can lead to subsequent yellow-orange discoloration (xanthoderma or carotenoderma) and their subsequent deposition in the outermost layer of skin. Carotenemia and carotenoderma is in itself harmless, and does not require treatment. In primary carotenoderma, when the use of high quantities of carotene is discontinued the skin color will return to normal. It may take up to several months, however, for this to happen.
Lycopene is a key intermediate in the biosynthesis of beta-carotene and xanthophylls.
Due to its strong color and non-toxicity, lycopene is a useful food coloring (registered as E160d) and is approved for usage in the USA, Australia and New Zealand (registered as 160d) and the EU.
A sunless-tanning product is tanning pills which contain beta-carotene.
However, chronic, high doses of synthetic β-carotene supplements have been associated with increased rate of lung cancer among those who smoke.
Canthaxanthin is most commonly used as a color additive in certain foods. Although the FDA has approved the use of canthaxanthin in food, it does not approve its use as a tanning agent. When used as a color additive, only very small amounts of canthaxanthin are necessary. As a tanning agent, however, much larger quantities are used. After canthaxanthin is consumed, it is deposited throughout the body, including in the layer of fat below the skin, which turns an orange-brown color. These types of tanning pills have been linked to various side effects, including hepatitis and canthaxanthin retinopathy, a condition in which yellow deposits form in the retina of the eye. Other side effects including damage to the digestive system and skin surface have also been noted. The FDA withdrew approval for use of canthaxanthin as a tanning agent, and has issued warnings concerning its use.
DHA (Dihydroxyacetone, also known as glycerone) is not a dye, stain or paint, but causes a chemical reaction with the amino acids in the dead layer on the skin surface. One of the pathways is a free radical-mediated Maillard reaction. The other pathway is the conventional Maillard reaction, a process well known to food chemists that causes the browning that occurs during food manufacturing and storage. It does not involve the underlying skin pigmentation nor does it require exposure to ultraviolet light to initiate the color change. However, for the 24 hours after self-tanner is applied, the skin is especially susceptible to ultraviolet, according to a 2007 study led by Katinka Jung of the Gematria Test Lab in Berlin. Forty minutes after the researchers treated skin samples with high levels of DHA they found that more than 180 percent additional free radicals formed during sun exposure compared with untreated skin. Another self-tanner ingredient, erythrulose, produced a similar response at high levels. For a day after self-tanner application, excessive sun exposure should be avoided and sunscreen should be worn outdoors, they say; an antioxidant cream could also minimize free radical production. Although some self-tanners contain sunscreen, its effect will not last long after application, and a fake tan itself will not protect the skin from UV exposure. The study by Jung et al. further confirms earlier results demonstrating that dihydroxyacetone in combination with dimethylisosorbide enhances the process of (sun-based) tanning. This earlier study also found that dihydroxyacetone also has an effect on the amino acids and nucleic acids which is bad for the skin.
The free radicals are due to the action of UV light on AGE (Advanced Glycation End-products) as a result of the reaction of DHA with the skin, and the intermediates, such as Amadori products (a type of AGE), that lead to them. AGEs are behind the damage to the skin that occurs with high blood sugar in diabetes where similar glycation occurs. AGEs absorb and provide a little protection against some of the damaging factors of UV (up to SPF 3), However, they do not have melanin's extended electronic structure that dissipates the energy, so part of it goes towards starting free radical chain reactions instead, in which other AGEs participate readily. Overall tanner enhances free radical injury. Although some self-tanners contain sunscreen, its effect will not last as long as the tan. The stated SPF is only applicable for a few hours after application. Despite darkening of the skin, an individual is still susceptible to UV rays, therefore an overall sun protection is still very necessary. There may also be some inhibition of vitamin D production in DHA-treated skin.
The color effect is temporary and fades gradually over 3 to 10 days. Some of these products also use erythrulose which works identically to DHA, but develops more slowly. Both DHA and erythrulose have been known to cause contact dermatitis.
Professional spraytan applications are available from spas, salons and gymnasiums by both hand-held sprayers and in the form of sunless or UV-Free spray booths. The enclosed booth, which resembles an enclosed shower stall, sprays the tanning solution over the entire body. The U.S. Food and Drug Administration (FDA) states when using DHA-containing products as an all-over spray or mist in a commercial spray "tanning" booth, it may be difficult to avoid exposure in a manner for which DHA is not approved, including the area of the eyes, lips, or mucous membrane, or even internally. DHA is not approved by the FDA for inhalation.
Many self tanners use chemical fragrances which may cause skin allergies or may trigger asthma. Furthermore, some of them contain parabens. Parabens are preservatives that can affect the endocrine system.
An opinion issued by the European Commission's Scientific Committee on Consumer Safety, concluding spray tanning with DHA did not pose risk, has been heavily criticized by specialists. This is because the cosmetics industry in Europe chose the evidence to review, according to the commission itself. Thus, nearly every report the commission's eventual opinion referenced came from studies that were never published or peer-reviewed and, in the majority of cases, were performed by companies or industry groups linked to the manufacturing of DHA. The industry left out nearly all of the peer-reviewed studies published in publicly available scientific journals that identified DHA as a potential mutagen. A study by scientists from the Department of Dermatology, Bispebjerg Hospital, published in Mutation Research has concluded DHA 'induces DNA damage, cell-cycle block and apoptosis' in cultured cells.
Tanning accelerators—lotions or pills that usually contain the amino acid tyrosine—claim that they stimulate and increase melanin formation, thereby accelerating the tanning process. These are used in conjunction with UV exposure. At this time, there is no scientific data available to support these claims.
Afamelanotide, a synthetic melanocyte-stimulating hormone analog, which induces melanogenesis through activation of the melanocortin 1 receptor, is another alternative on the horizon. A 1991 clinical Investigational new drug trial conducted at the Department of Internal Medicine, University of Arizona Health Sciences Center with afamelanotide (then known by its amino acid formula [Nle4, D-Phe7] (NDP)-alpha-melanocyte-stimulating hormone) with 28, "healthy white men" who used a, "high-potency sunscreen during the trial" and concluded, "Human skin darkens as a response to a synthetic melanotropin given by subcutaneous injection. Skin tanning appears possible without potentially harmful exposure to ultraviolet radiation." 
Afamelanotide in a subcutaneous implant form is currently undergoing clinical trials and being developed by a company in Australia.
Other melanogenesis stimulants
Vitamin D metabolites, retinoids, melanocyte-stimulating hormone, forskolin, isobutylmethylxanthine, diacylglycerol analogues, and even cholera toxin, all stimulate the production of melanin. 9-cis retinoic acid is a potential treatment for vitiligo.
Forskolin is a natural compound that has been shown to create a natural tan by stimulating melanin production in mice. It is derived from the root of the Indian Coleus, from the foothils of the Himalaya.
Bronzers are a temporary sunless tanning or bronzing option. These come in powders, sprays, mousse, gels, lotions and moisturizers. Once applied, they create a tan that can easily be removed with soap and water. Like make-up, these products tint or stain a person's skin only until they are washed off.
They are often used for "one-day" only tans, or to complement a DHA-based sunless tan. Many formulations are available, and some have limited sweat or light water resistance. If applied under clothing, or where fabric and skin edges meet, most will create some light but visible rub-off. Dark clothing prevents the rub-off from being noticeable. While these products are much safer than tanning beds, the color produced can sometimes look orangey and splotchy if applied incorrectly.
A recent trend is that of lotions or moisturizers containing a gradual tanning agent. A slight increase in color is usually observable after the first use, but color will continue to darken the more the product is used.
Air brush tanning is a spray on tan performed by a professional. An air brush tan can last five to ten days and will fade when the skin is washed. It is used for special occasions or to get a quick dark tan. At-home airbrush tanning kits and aerosol mists are also available.
Since the coloration that forms does not provide much protection against UV, and the effect only lasts for a few hours, tanners usually contain a sunscreen. The ingredients known to offer appropriate protection are titanium dioxide, zinc oxide, or avobenzone. However, when avobenzone is irradiated with UVA light, it generates a triplet excited state in the keto form which can either cause the avobenzone to degrade or transfer energy to biological targets and cause deleterious effects. It has been shown to degrade significantly in light, resulting in less protection over time. The UV-A light in a day of sunlight in a temperate climate is sufficient to break down most of the compound. Data presented to the Food and Drug Administration by the Cosmetic, Toiletry and Fragrance Association indicates a -36% change in avobenzone's UV absorbance following one hour of exposure to sunlight.
If avobenzone-containing sunscreen is applied on top of tanner, the photosensitizer effect magnifies the free-radical damage promoted by DHA, as DHA may make the skin especially susceptible to free-radical damage from sunlight, according to a 2007 study led by Katinka Jung of the Gematria Test Lab in Berlin. Forty minutes after the researchers treated skin samples with 20% DHA they found that more than 180 percent additional free radicals formed during sun exposure compared with untreated skin.
September 2012 also saw a surge in debate within the United Kingdom regarding the inhalation of DHA through spray tanning. While the quantities inhaled would have to be considerably higher than an average consumer or even spray tan technician would be exposed to, press coverage on the issue has resulted in increased consumer diligence with regard to the level of DHA and other ingredients in their spray tanning products, and a move toward more naturally-derived spray tan solutions. An EU Directive published by the Scientific Committee of Consumer Safety to eventually limit DHA content of spray tan products to 14% has also been cited within this discussion. Risks of inhaling or ingesting DHA are not known. People are advised to close their eyes or protect them with goggles and to hold their breath or wear nose plugs while they have a spray-on tanning applied.
In the report released to ABC News, FDA scientists concluded that DHA does not stop at the outer dead layers of skin. They wrote: "The fate of DHA remaining in skin is an important issue, since high DHA skin levels were found." They added that tests they performed revealed that much of the DHA applied to skin actually ended up in the living layers of skin. They concluded: "This leaves about 11 percent of the applied DHA dose absorbed remaining in the [living] epidermis and dermis." Any absorption into the living areas of the skin could be pose a potential risk, even if none of it made it into the bloodstream, said Dr. Darrell Rigel, an NYU professor of dermatology. The fact that some does potentially get into the bloodstream raised additional red flags for him that he said needed to be further explored. Rigel was especially concerned for repeated users of the product and those in higher-risk groups such as pregnant women or young children. "What you showed me certainly leads me to say I have to rethink what I'm doing and what I'm saying because there's ... a real potential problem there," he said. "I feel that I must give my patients the information that you've given to me, because I think it is valid." Before he read all of the papers, Rigel said, he would "tell my patients what every other dermatologist tells them: 'If you want to be tanned, [tanning with DHA] is effective, it's not being absorbed and there's no long-term problems.' After reading these papers, I'm not sure that's true anymore." 
A toxicologist and lung specialist at the University of Pennsylvania's Perelman School of Medicine (Dr. Rey Panettieri) has commented, "The reason I'm concerned is the deposition of the tanning agents into the lungs could really facilitate or aid systemic absorption -- that is, getting into the bloodstream. These compounds in some cells could actually promote the development of cancers or malignancies, and if that's the case then we need to be wary of them." A study by scientists from the Department of Dermatology, Bispebjerg Hospital, published in Mutation Research has concluded DHA 'induces DNA damage, cell-cycle block and apoptosis' in cultured cells.
Many self tanners use chemical fragrances which may cause skin allergies or may trigger asthma. Furthermore, some of them contain parabens. Parabens are preservatives that can affect the endocrine system.
Tanners can stain clothes. It is therefore important to look for fast drying formulas and wait around 10 to 15 minutes for the product to dry before dressing.
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