Ultraviolet A sunscreen evaluations in normal subjects.

We have used a specially modified xenon arc solar simulator to examine ultraviolet A (UVA) protection of a research sunscreen formulation. UVA doses were given to sunscreen-protected and unprotected skin with the use of irradiance values of 50 mW/cm2 and 100 mW/cm2. Erythemal responses were evaluated 5.2 +/- 0.9 hours later and again 24.4 +/- 1.8 hours later. The overall mean unprotected UVA minimal erythema dose (MED) was 23.6 joules/cm2 (SD = 4.8) and the mean UVA protection factor (APF) was 3.2 (SD = 0.78). Neither irradiance nor evaluation time significantly affected MED or APF. These preliminary findings indicate that the modified solar simulator permits convenient determination of sunscreen APF. The APF of a sunscreen is analogous to SPF: APF refers to UVA protection, while SPF refers to protection from the entire solar spectrum, predominantly from the effects of UVB.