Wavelength Dependence for DNA Photodamage in Human Skin In Vivo

Action spectra for DNA photodamage were determined in different human epidermal layers in situ. Skin was irradiated with varying doses of monochromatic UVR (280-360 nm). Sections from punch biopsies taken immediately after exposure were stained with a monoclonal antibody against thymine dimers and quantified by image analysis. Dimers were measured at two basal layer regions, the mid and the upper epidermis. Dose-response curves were used to generate four action spectra, all of which had maxima at 300 nm. These spectra were independent of epidermal layer between 300 and 360 nm, indicating comparable epidermal transmission at these wavelengths. However, there was a marked effect of epidermal layer between 280-300 nm, showing relatively poor transmission of 280 and 290 nm to the basal layer. These data indicate that solar UVB (~295-320 nm) damages basal cells more than predicted from transmission data obtained from human epidermis ex vivo.