UVA-induced erythema, pigmentation, and skin surface temperature changes are irradiance dependent

Human cutaneous erythemogenic and melanogenic responses to long-wave (UVA) ultraviolet radiation were investigated using irradiances ranging from 5-50 mW/cm2. Skin surface temperature changes resulting from the different irradiances were also compared. In general, threshold doses for erythema and pigmentation were higher when UVA was administered at the lowest irradiance (5 mW/cm2) than at the highest (50 mW/cm2). Erythema was maximal immediately after exposure to UVA. The most intense responses (erythema with edema, or intense pigmentation) were induced more frequently by the highest irradiance. Components of both the erythema and the pigment response to UVA are therefore irradiance-dependent. The greatest increase in skin surface temperature was observed after exposure to the highest irradiance.