Like cigarette smoking, a deep, dark tan was once very desirable. A generation ago, a teenager might have spent hours on a beach, skin glistening with oil, maybe even using a reflecting device to concentrate sun exposure on the face. Today, as they lather on sunblock, many of these people realize that the tans of yesterday may cause cancer tomorrow.

Just four hours of unprotected sunbathing has immediate and lasting effects on the skin. The ultraviolet radiation alters collagen and elastin and dilates blood vessels in the dermis. A few days later, the outer skin layer may blister and peel. Cells that peel off have undergone programmed cell death, a protective mechanism to rid the body of cells possibly turned cancerous from environmental exposure. People with the inherited disorder xeroderma pigmentosum lack DNA repair enzymes, and can never venture outside without being completely covered by clothing or sunblock. Even the briefest exposure can provoke a sea of freckles to bloom, some of which may become cancerous.

Skin cancer usually arises from nonpigmented epithelial cells within the deep layer of the epidermis or from pigmented melanocytes. Skin cancers originating from epithelial cells are called cutaneous carcinomas (basal cell carcinoma); those arising from melanocytes are cutaneous melanomas (melanocarcinomas or malignant melanomas).

Cutaneous carcinomas are the most common type of skin cancer, occurring most frequently in light-skinned people over forty years of age. These cancers usually appear in persons who are exposed to sunlight regularly, such as farmers, sailors, athletes, and sunbathers.

Cutaneous carcinoma often develops from hard, dry, scaly growths (lesions) that have reddish bases. Such lesions may be either flat or raised, and they adhere firmly to the skin, appearing most often on the neck, face, and scalp. Fortunately, cutaneous carcinomas are typically slow growing and can usually be cured completely by surgical removal or radiation treatment.

Cutaneous melanomas are pigmented with melanin, often with a variety of colored areas--variegated brown, black, gray, or blue--arranged haphazardly. They usually have irregular rather than smooth outlines.

Cutaneous melanomas may appear in young adults as well as in older ones, and seem to be caused by short, intermittent exposure to high-intensity sunlight. Thus, risk of melanoma increases in persons who stay indoors but occasionally sustain blistering sunburns.

Cutaneous melanomas occur most often in light-skinned people who burn rather than tan. The cancer usually appears in the skin of the trunk, especially the back, or the limbs, arising from normal-appearing skin or from a mole (nevus). The lesion spreads through the skin horizontally, but eventually may thicken and grow downward into the skin, invading deeper tissues. If the melanoma is removed surgically while it is in its horizontal growth phase, it may be arrested. Once it thickens and spreads into deeper tissues, unfortunately, it becomes difficult to treat. The survival rate with conventional treatment is very low. However, genetic researchers are excited about a form of gene therapy in which genes injected directly into melanoma cells direct the cells to produce surface proteins that attract cancer-fighting biochemicals produced by cells of the immune system.

For reasons that are not well understood, the incidence of melanoma within the U.S. population has been increasing rapidly for the past twenty years. To reduce the chances of occurrence, avoid exposing the skin to high-intensity sunlight, use sunscreens and sunblocks, and examine the skin regularly. Report any unusual lesions--particularly those that change in color, shape, or surface texture--to a physician.

Replacements for natural suntanning may be ineffective or dangerous. Sunless tanning agents do not cause the skin to tan at all, but merely dye it temporarily. Tan accelerators, according to manufacturers, are nutrients that supposedly increase melanin synthesis in the sunlight, but there is no scientific proof that they work. Tanning booths may be dangerous. Even those claiming to be safe because they emit only partial ultraviolet radiation may cause skin cancer.

Enjoy the sun--but protect yourself!

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