Unraveling the mystery of melanin: Does a tan protect skin from sun damage or contribute to it?

Abstract

Once, many people innocently enjoyed the lazy days of summer by working on a tan. A deep bronze tone, they believed, would act like a natural sunscreen, protecting their skin for the rest of the season. Indeed more than a decade ago, test-tube studies on melanin, the modified protein that darkens skin, showed that it can block some of the harmful effects of ultraviolet radiation. Other studies, however, painted a less sunny picture of the dark protein. They indicated that melanin can itself play a role in certain chemical processes that damage DNA and other molecules in cells. This damage, some scientists speculate, is one of the mechanisms by which ultraviolet light can lead to skin cancer. Chemists are now trying to determine what melanin actually does in the skin. Although most people have heard of melanin, scientists don't fully understand its structure and behavior, says John D. Simon of Duke University in Durham, N.C. Melanin's photochemical properties might explain why certain people are more susceptible to skin cancer than others. People with fair skin and hair generally have a greater risk of skin cancer than do people with dark skin and hair. The incidence of skin cancer is 10 times higher in whites than in African Americans, for example. By examining melanin's response to light in test-tube experiments, Simon and other researchers hope to reveal its true colors. Is it photoprotective or photosensitizing? asks Simon. To some extent, both must be right. E ven though people in the United States use more sunscreen than ever before, skin cancer rates continue to rise (SN: 6/6/98, p. 360). Melanoma, the most deadly form of skin cancer, is a dis-