Synopsis

In vitro spectral transmission measurements using excised human epidermis as the substrate were used to determine the photoprotection provided by physical and organic chemical sunscreens encompassing a wide range of sun protection factor (SPF). The measured SPFs were in good agreement with the quoted SPFs of the products. This in vitro technique using human epidermis could prove reliable for evaluating the SPF of high-protection sunscreens for which in vivo assay is problematic due to the impractically long irradiation times to achieve erythema on sunscreen-protected skin. We also compared our calculated SPFs, which assumed a natural sunlight spectrum, with those that would have been obtained assuming a xenon-arc solar simulator spectrum. We found that for products with relatively low UV-A absorption, the use of a solar ß simulator for in vivo testing overestimates the SPF that would be expected in sunlight