Sun Signs

Since MoJo’s May/June 1993 cover story, “Beach Bummer,” which alleged that most sunscreens do not prevent malignant melanoma skin cancer, and may actually promote the potentially fatal cancer, two scientific reports on the subject have been published. The first, in the October 14 New England Journal of Medicine, described an Australian study in which sunscreen users showed a significant reduction in solar keratoses, a risk factor for skin cancer. Sunscreen did not prevent cancer; it simply reduced the likelihood of developing one of ten risk factors.

The U.S. media overstated the study’s findings and neglected to report that the sunscreen used in the study was nothing like what most Americans apply. Until recently, most sunscreens available in the U.S. blocked just one type of ultraviolet light–UV-B, the rays that cause sunburn. Deeper-penetrating UV-A rays, on the other hand, are barely blocked at all. Even “broad-spectrum” sunscreens only block about one-third of UV-A. But the sunscreen used in the study blocked 94 percent of it.

MoJo’s article focused on the theory that UV-A might be the culprit in the melanoma epidemic of the last twenty years. At the time of the article, there was no animal model to prove this. But last July, as reported in Proceedings of the National Academy of Sciences, researchers at Brookhaven National Laboratories induced melanoma in fish. “In this animal model,” the researchers wrote, “90 percent to 95 percent of melanoma may be attributed to UV-A. . . . It is reasonable to extend this conclusion to humans. Sunscreens effective in the UV-B region would not protect against melanoma induction by sunlight.”

Sunscreens that largely block UV-A include Photoplex and Shade UVA Guard.