Sunless tanning
Sunless tanning refers to the effect of a suntan without exposure to the Sun. Sunless tanning involves the use of oral agents, or creams, lotions or sprays applied to the skin. Skin-applied products may be [|skin-reactive agents] or temporary bronzers.
Sunless tanning has emerged as an alternative to UV exposure, which has been linked to increased risk of skin cancer.
The chemical compound dihydroxyacetone is used in sunless tanning products in concentrations of 3%-5%. DHA concentration is adjusted to provide darker and lighter shades of tan. The reaction of keratin protein present in skin and DHA is responsible for the production of pigmentation.
Oral agents (carotenoids)
A 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 a more attractive skin tone than suntan. Carotenes also fulfil the function of melanin in absorbing 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 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 and their subsequent deposition in the outermost layer of skin. Carotenemia, or 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.Lycopene may be the most powerful carotenoid quencher of singlet oxygen.
Due to its strong color and non-toxicity, lycopene is a useful food coloring and is approved for usage in the US, Australia and New Zealand and the EU.
Beta-carotene
Sunless-tanning pills often contain β-carotene. The American Cancer Society states that "Although the US Food and Drug Administration has approved some of these additives for coloring food, they are not approved for use in tanning agents." Also that "They may be harmful at the high levels that are used in tanning pills."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 and has issued warnings concerning its use. When used as a color additive, only very small amounts of canthaxanthin are needed. 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.Skin-reactive agents
DHA-based products
DHA 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 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 as a result of the reaction of DHA with the skin, and the intermediates, such as Amadori products, 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, 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 spray tan applications are available from spas, salons and gymnasiums by both hand-held sprayers and in the form of sunless or UV-Free spray booths. Spray tan applications are also available through online retail distribution channels and are widely available to purchase for in home use. The enclosed booth, which resembles an enclosed shower stall, sprays the tanning solution over the entire body. The U.S. Food and Drug Administration 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.
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.
SIK-inhibitors
A novel class of compounds has been found to stimulate melanogenesis in a mechanism that is independent from α-melanocyte-stimulating hormone activation of the melanocortin 1 receptor. This is accomplished via small molecule inhibition of salt-inducible kinases. Inhibition of SIK increases transcription of MITF which is known to increase melanin production. Work published in June 2017 has demonstrated compounds that have efficacy when applied topically to human skin. These compounds are still however in pre-clinical stages of development. Future directions may include the incorporation of SIK-inhibitor compounds with traditional UV-blocking sunscreens to minimize UV-related DNA damage in the short term while providing longer term protection through endogenous melanin production.Tyrosine-based products
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.Melanotan peptide hormones
The role of alpha-melanocyte-stimulating hormone in promoting melanin diffusion has been known since the 1960s. In the 1980s, scientists at University of Arizona began attempting to develop α-MSH and analogs as potential sunless tanning agents, and synthesized and tested several analogs, including afamelanotide, then called melanotan-I.In the European Union and United States, afamelanotide is indicated for the prevention of phototoxicity in adults with erythropoietic protoporphyria. Afamelanotide is also being investigated as a method of photoprotection from in the treatment of polymorphous light eruption, actinic keratosis and squamous cell carcinoma. Bremelanotide is used for the treatment of generalized hypoactive sexual desire disorder in premenopausal women.
To pursue the tanning agent, melanotan-I was licensed by Competitive Technologies, a technology transfer company operating on behalf of University of Arizona, to an Australian startup called Epitan, which changed its name to Clinuvel in 2006.
A number of products are sold online and in gyms and beauty salons as "melanotan" or "melanotan-1" which discuss afamelanotide in their marketing. The products are not legal in any jurisdiction and are dangerous. Starting in 2007 health agencies in various counties began issuing warnings against their use.