Sunscreen protection against UV-induced pyrimidine dimers in DNA of human skin in situ.

We have determined the ability of a chemical sunscreen with a sun protection factor (SPF) of 15 to protect human skin from ultraviolet (UV) radiation-induced DNA damage. The DNA damage was susceptible to cleavage by Micrococcus luteus UV endonuclease, which recognizes pyrimidine dimers in DNA. An alkaline agarose gel electrophoresis method was used to quantify the number of pyrimidine dimers in nonradioactive DNA from skin biopsies of 5 individuals irradiated with UV from a solar simulator. After exposure to an equivalent dose of UV, the number of pyrimidine dimers was 0.8 per 10(7) bases in sunscreen-treated skin as compared with 32 dimers per 10(7) bases in untreated skin. This assay provides a means of determining the efficacy of sunscreens in protecting skin from UV-induced DNA damage.