Ultraviolet radiation induced pyrimidine dimers in DNA have been shown to be involved in the tumorigenesis process. The variability in numbers of pyrimidine dimers induced with a broadband UVB (290-320 nm) lamp in skin of different volunteers has previously been shown to be a function of skin type. We have determined an action spectrum for induction of pyrimidine dimers in the DNA of human skin for volunteers of skin type I (sun sensitive) and skin type IV (fairly sun insensitive). The peak of this action spectrum is near 302 nm and decreases rapidly at both longer and shorter wavelengths. The number of pyrimidine dimers induced by a given wavelength was always greater in skin type I than in skin type IV. The frequency of pyrimidine dimers at an erythemogenic dose of UV was found to vary dramatically as a function of wavelength.
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