Sunscreens prevent ultraviolet photocarcinogenesis.

Sunscreens of low or high sun protection factors (SPF*) were tested for their ability to inhibit ultraviolet (UV) carcinogenesis in two varieties of hairless mice. Low protection (SPF = 2) reduced by 50% the number of albino animals developing tumors. High protection (SPF =15) prevented tumor formation. Tumorigenesis was totally prevented in the lightly pigmented variety with either sunscreen, demonstrating the added protection of melanin. In mice and man, UV-induced cancer is a cumulative process. Reducing the amount of UV light reaching the basal layer will retard that process.