Testing the efficacy of sunscreens: effect of choice of source and spectral power distribution of ultraviolet radiation, and choice of endpoint.

The problems inherent in testing the protective efficacy of sunscreens are reviewed. Of primary importance are: the spectral power distribution of the test light source, which should simulate the ultraviolet radiation of midlatitude, midsummer sunlight; definition of minimal erythema of skin, and equilibration of light source and filters prior to testing.