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In general, those most vulnerable to skin cancer are the light-skinned, light-eyed people of north European extraction, particularly those with red or blond hair and freckled skin that reddens and burns easily, blisters and peels. Caucasians with dark hair and eyes and more even pigmentation, as well as Hispanics and Asians, are somewhat less susceptible, and blacks rarely develop either carcinomas or melanomas. The rate of melanoma among blacks, while increasing, is only one-fiftieth that of whites.
Dark pigmentation is obviously protective. The rare melanomas found among blacks develop almost exclusively in areas of lighter skin not usually exposed to the sun: palms of the hands, soles of the feet, under fingernails and even in the mouth. This leads experts to believe that melanomas among blacks are largely genetic.
Geography also plays a role in skin cancer. Equatorial regions, where the midday sun beams down from directly overhead, receive the most intense ultraviolet radiation. Farther north or south, solar rays strike the earth at a more oblique angle, taking a longer passage through the atmosphere, where the ozone layer absorbs more of the ultraviolet light before it can reach the surface.
Skin-cancer statistics vary accordingly. For example, the National Cancer Institute reports that from 1983 to 1987, Atlanta's melanoma rate averaged 11.6 per 100,000 people each year, while the more northerly Detroit's average was only 7.4. In Tucson, Ariz., which is close to Atlanta in latitude but has many more sunny days, the rate soars to 19, the highest in the U.S.
The migration to tropical climes of people with racial origins in higher, less sunny latitudes has also led to rising rates of skin cancer. A survey of nonmelanoma skin cancers in Hawaii, for example, concluded that Japanese residents of the island of Kauai were 88 times more likely to develop a skin malignancy than Japanese living in Japan. And in subtropical Australia, which was settled largely by the fair-skinned English and Irish, the skin-cancer rate is the highest in the world. Two out of three Australians will develop at least one skin cancer during their lifetime.
That remarkable statistic helps explain why Australia is a leader in anti- skin cancer campaigns. Each year during National Skin Cancer Awareness Week, literature and posters are distributed and dermatologists conduct free skin-cancer screenings. In the state of Victoria, lifeguards are used as role models. They sit in shaded areas, pass out skin-cancer literature, don hats and wear T shirts emblazoned with the slogan SLIP! SLOP! SLAP! -- which practically everyone Down Under understands to mean "Slip on a shirt. Slop on some sunscreen. Slap on a hat."
Awareness of skin cancer is rising in the U.S., largely through the efforts of the Skin Cancer Foundation and the American Cancer Society, which attempt to spread the word through posters, pamphlets, newspaper ads and an occasional billboard. Hollywood may help. Some of today's most popular female stars, including Kim Basinger and Geena Davis, shun the sun, projecting a pale beauty that could influence a new generation. Manufacturers of sunscreens seem to have caught on. Store shelves these days display more screens with sun- protection factors of 15, 25 and 30 than with the once familiar 4 and 8 ratings.