The evidence that ultraviolet radiation causes skin cancer is overwhelming and convincing. Despite this information, the use of indoor tanning deviceswhich emit ultraviolet (UV) light, both in tanning parlors and at home, has never been more popular. Indoor tanning is big business, with tanning trade publications reporting this as a $2 billion-a-year industry in the United States. According to industry estimates, 28 million Americans are tanning indoors annually at about 25,000 tanning salons around the country.

Is It Healthy?

Over the last year, the indoor tanning industry has taken an aggressive stand, claiming that not only is indoor tanning harmless, but that it is actually healthy.
Tanning is an acquired darkening of the skin in response to ultraviolet radiation. The exact mechanism is unknown, though researchers have been able to induce tanning by applying fragments of DNA to animal and human skin. Not all people are capable of developing a tan in response to UV radiation exposure: Very fair-skinned people simply burn and freckle. In those who can tan, the brown pigment melanin is produced and distributed in the superficial portion of the skin (the epidermis) in the days following exposure. The development of this pigment minimally protects the skin against further damage from UV radiation.
This rather minor protection is cited to support the suggestion that a tan is healthy; that is not the case. In fact, the important point is that damage to the DNA must have been produced to create a tan in the first place.
The wisdom of indoor tanning for cosmetic purposes has been repeatedly questioned by organized medicine. This criticism reached a peak in December, 1994, when the American Medical Association (AMA) adopted a resolution calling for a ban on the sale and use of tanning equipment for non-medical purposes, i.e., cosmetic. However, the United States Federal Trade Commission (FTC), which regulates the sale and marketing (but not the use) of indoor tanning equipment, declined to institute such a ban. The FTC did not accept the AMA's position, and in fact moved in the other direction, prohibiting the industry from marketing indoor tanning for any purpose other than cosmetic. It cannot make health claims. The tanning industry has requested a change in this regulation and is actively seeking the ability to market the "health benefits" of indoor tanning. The case for such benefits is very weak, while the case for the risks of indoor tanning is very strong.

The Rise of Indoor Tanning

The social desirability of a tan is a modern phenomenon, beginning in the 1920s when the French designer Coco Chanel decreed it as a fashion look. The concept of obtaining a tan without going outdoors became increasingly attractive. However, early indoor tanning units emitted the most damaging portions of the ultraviolet spectrum, UVC and UVB, and were plagued by safety problems. In the 1970s, medical devices that emit principally UVA were developed and quickly adopted for modern indoor tanning. The biological effects of UVA were less obvious than those of UVB, which is responsible for skin reddening, or UVC and these devices were touted as offering a "safe" tan.
It soon became apparent that UVA exposure could cause the same problems as UVB, namely sunburns, wrinkles (photoaging), and skin cancer. The UVA-emitting devices also were not very effective at inducing a tan. And so, the idea of a "safe" UVA tan, so highly promoted by the indoor tanning industry just a few years ago, is now gone. It was not abandoned for scientific reasons, but purely out of the market-driven desire for darker and faster tanning than UVA could induce.
The next step was the development of indoor tanning devices that contain a mixture of UVA and UVB, simulating the mixture found in the sun. These are the ones in use today.

Indoor Tanning and Skin Cancer

What then is the evidence that associates indoor tanning with skin cancer?
Tanning Trends magazine, a trade publication, writes: "Moderate tanning has never been linked scientifically to skin cancer. In fact, by helping people tan with a reduced incidence of sunburn, indoor tanning may reduce your risk of ever contracting skin cancer." Indeed, quite the reverse is true: By increasing exposure to carcinogenic UV rays, the risk of skin cancer is increased.
The association of sunlight and the development of skin cancer was first appreciated by P.G. Unna of Berlin, who published a report on the topic in 1894. Since that time an enormous volume of epidemiologic, clinical, and laboratory studies have supported a causal role of the ultraviolet portion of the sun's rays in the development of skin cancer. UV radiation seems to be the cause of all three common skin cancers -- basal cell carcinoma, squamous cell carcinoma, and melanoma. It is thought to induce skin cancers by three mechanisms: First, ultraviolet light directly damages DNA leading to mutations; second, it produces activated oxygen molecules that in turn damage DNA and other cellular structures; and third, it leads to a localized immunosuppression, thus blocking the body's natural anti-cancer defenses.

Exposure Patterns

Even the indoor tanning industry admits ultraviolet radiation can cause skin cancer provided that it produces an actual burn. However, industry spokespeople point out that the pattern of sun exposure that causes skin cancer, in particular melanoma and basal cell carcinoma, is not consistent with indoor tanning practices. For a given amount of UV light, the industry argues there is a difference between receiving the energy in many small doses that lead to a tan versus a few big doses that produce a burn.
Squamous Cell Carcinoma (SCC): Epidemiologic studies in humans do not give much information about patterns of exposure. Such studies may require patients to remember sun exposure habits from 40 years ago. With this limitation in mind, it appears that there is a somewhat linear relationship with cumulative sun exposure and the development of squamous cell carcinoma. The more sun, the more SCC, even when the sun exposure occurs on a chronic low-dose basis as received by a regular tanner.
Melanoma: This form of cancer follows a somewhat different pattern. Epidemiologic studies have suggested that intense intermittent exposure resulting in sunburn, especially in childhood, is most likely to lead to melanoma development.
Basal Cell Carcinoma (BCC): It now appears that basal cell carcinoma follows a pattern more similar to melanoma than that of squamous cell carcinoma.

Sunburned Animals

Laboratory studies with experimental animals allows the carcinogenic exposure patterns to be precisely examined. A variety of experimental animals readily develop SCC following ultraviolet light exposure, and much of our knowledge of skin cancer has been obtained from them. When UV light is given in many small doses designed to simulate what indoor tanners might receive, experimental animals actually developed more SCCs than when the same amount of energy was delivered in a few big doses resulting in sunburns.
Similarly, wrinkling, an important element of photoaging, is greater in the hairless albino mouse when a given dose of UVB is delivered in smaller daily fractions, as in a tanning salon. Thus for the development of squamous cell carcinoma and photoaging, tanning is actually more dangerous than burning.
Unfortunately, until very recently there has been no good animal model for melanoma or basal cell carcinoma, so our knowledge has been principally derived from retrospective epidemiologic studies in human populations and is thus incomplete.
Research has now advanced with the discovery that the South American opossum Monodelphid domestica is capable of developing melanocytic tumors and it has been used as an animal model for melanoma. Studies with this animal suggest that multiple low doses of UV radiation are more effective than high doses in inducing melanoma.

Tanning vs. Sunburns

The association of sunburns with the development of melanoma has led the indoor tanning industry to suggest that if only these people were tan, they would not sunburn, and thus their melanoma risk would decrease. This concept is erroneous. First, it remains unclear whether the "sunburns only" hypothesis of melanoma development is true. Second, tans acquired at indoor tanning parlors have been studied and have a very poor ability to prevent sunburning. Finally and most important, very fair-skinned people are at the highest risk for melanoma, and they tan poorly or not at all, and burn whether at the beach or at the tanning salon. For this high risk group, the burn versus tan debate is irrelevant.
While it is clear that ultraviolet light causes all three types of skin cancer, in the case of melanoma and basal cell carcinoma, it is not known whether burning or tanning is more carcinogenic. Even if burns are more carcinogenic than tanning (which clearly is not true for the development of squamous cell carcinoma), with currently available knowledge it is not reasonable to encourage tanning to prevent carcinogenic sunburns. Patrons can and frequently have burned themselves at indoor tanning parlors. Furthermore, indoor tanning provides little protection against burns from the sun. Most important, the tanning process itself, even in the absence of burning, injures the skin.

Risks of Indoor Tanning

Epidemiologic and clinical studies of indoor tanners themselves are now becoming available to help better assess the risks. Proliferations of melanocytes (pigmented cells) known as lentigines have been seen in indoor tanners. These proliferations are significant in that they demonstrate some of the cytologic atypia and architectural features seen in dysplastic nevi, which are risk factors for melanoma development. Studies examining the development of melanoma in indoor tanners have produced mixed results. Four early studies, reviewed in reference, found little, or statistically insignificant, association between indoor tanning and melanoma. However, six more recent, rigorously designed studies have found an association between indoor tanning and the development of melanoma. Of particular note, no study has ever suggested a protective role for indoor tanning. While these studies remain inconclusive, they were enough for the American Medical Association to call for a ban on tanning beds.

Public Policy on Tanning

Physicians and medical groups around the world have undertaken extensive campaigns to decrease excessive exposure to ultraviolet light in order to reduce the current epidemic of skin cancer. These efforts have been successful at educating the public. Surveys show there is increasing awareness that ultraviolet light causes skin cancer. Despite this knowledge, tanning indoors and outdoors is more popular than ever. Most studies suggest young women are the most frequent patrons of tanning salons. The development of photoaging and skin cancer will take years to become apparent in these young tanners, while the perceived social value of a tan is apparent immediately. It seems likely the indoor tanning industry will continue to actively market its services, including the rather dubious claim that indoor tanning is not only harmless but is healthy. Regulation of the tanning industry at the state and national level is important, especially to prevent false health claims from being made. Physicians and those concerned about preventing skin cancer can and should continue to play a major role in educating the public about the dangers of tanning, especially directing efforts towards young tanners.