The influence of UVA and visible radiation on acute damage by short-wave UVR (lambda less than 320 nm).

The influence of UVA and visible radiation on the acute damage by short-wave ultraviolet radiation (UVR) (lambda less than 320 nm) was investigated in human volunteers, using delayed erythema and sunburn cell production as markers of injury. It was found that subsequent exposure to UVA + visible radiation produced a significant reduction of the threshold erythema dose by short-wave UVR, in a dose-dependent manner. Subsequent exposures to varying doses of UVA + visible radiation, as well as to visible light alone failed to influence sunburn cell production. It is concluded that there is a positive interaction between short-wave UVR and UVA in the induction of delayed erythema, but this may not apply to epidermal cell injury. Photorecovery was not observed.