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Does sunscreen increase or decrease melanoma risk?

Can using sunscreen help prevent melanoma, one of the deadliest forms of cancer? Conversely, does using sunscreen increase the risk of developing melanoma?

That's the controversy researchers across the country have been attempting to resolve. It is an urgent matter: in Western countries in particular, melanoma is increasing faster than any other cancer. In the U.S., the number of new cases of melanoma has more than doubled in the past 20 years.

Martin Weinstock, MD, who works in the dermatoepidemiology unit of the VA Medical Center in Providence, has been studying the relationship for years. In 1999, he published an article in the Journal of Investigative Dermatology Symposium Proceedings, which stated that sunscreen use should be continued while researchers investigate the exact cause of melanoma. Weinstock painstakingly reviewed dozens of studies for evidence of any link between sunscreen use and either an increase or decrease in melanoma. He has furthered this discussion in several recent articles in Photodermatology, Photoimmunology and Photomedicine and Controversies in Photodermatology published last year.

Prevent sunburn, prevent melanoma?
Although it is known that increased exposure to sun is a risk factor for melanoma, researchers are not sure which wavelength of ultraviolet radiation—UVA, UVB, or both—causes the cancer. If so, using sunscreen with a sun protection factor (SPF) of 15 or higher could be effective in preventing sunburn and therefore melanoma. However, Weinstock notes, the cause or "action spectrum" of melanoma remains unknown and to make that connection is perhaps premature.

Does sunscreen give false confidence?
Another theory suggests that people who use sunscreen will stay in the sun longer and in doing so increase their melanoma risk by increasing exposure to UVA. In his own research, Weinstock did not find this to be true.

People who used sunscreen were more likely to use other protective measures, such as wearing protective clothing and staying out of the sun at peak times, he noted. He wrote he doubted staying in the sun longer while wearing sunscreen could result in an increase in melanoma cases, at least in places like New England where there is not enough ultraviolet radiation reaching the beaches, even in the middle of the summer, to cause a sunburn while wearing sunscreen.

The role of vitamin D
Weinstock also addressed the concern that using sunscreen will lead to a lack of vitamin D. Vitamin D is produced in the skin using ambient ultraviolet radiation, as well as taken in foods. Some have suggested that vitamin D may inhibit melanoma. His review showed no such connection, however, on any count.

Problems with studies
Weinstock notes that 12 epidemiological studies of the relation of sunscreen use to melanoma risk have been published, with another study known to the author. Of these,

• Three showed a decreased risk of melanoma
• Four showed an increased risk
• Six were inconclusive

Weinstock gave several reasons for these inconsistencies, including:

• Difficulty of study participants in recalling sun exposure and sunscreen use
• Fifteen to 20-year lag time between sunscreen use and development of melanoma
• Lack of effective sunscreen (with SPF of 15 or more) before 1987.
• A bias against publishing negative effects
• Poorly designed studies that did not factor out skin types and other known risk factors for melanoma

Known risk factors
In addition to sun exposure and fair skin, there are other known risk factors for melanoma of which people should be aware. Anyone with risk factors should be checked regularly by a doctor who is familiar with diagnosing melanoma.

• Family history, especially if you have two or more relatives with the disease.
• A personal history of melanoma. If you've had melanoma, you are at higher risk to have it again.
• “Dy