Ultraviolet radiation-induced erythema in human skin.

We have evaluated UVR-induced erythema in previously unexposed buttock skin of volunteers of skin types I, II, III, and IV. Studies were done with solar-simulated radiation (SSR), UVB, and UVAI and we determined the just perceptible minimal erythema dose (MED) and, in some cases, quantified erythema with a reflectance device. The results show that there is a trend for increased SSR MED with skin type, with the MED of skin type IV being approximately twice that of skin type I, a smaller difference than one might have expected. However, there is a very considerable overlap of MED between skin types which shows that MED is a very poor indictor of skin type. Quantitative dose-response and time course studies with SSR and UVAI showed broadly similar responses when comparable MED-based exposures were given. We used our data to test the new concept of the standard erythema dose (SED) with two different erythema action spectra, and confirmed that the SED approach works with the different UVR sources that we studied.