A 16-week human clinical study was carried out to determine the ability of antioxidants in a cosmetic vehicle to inhibit the induction of lipid peroxidation in stratum corneum lipids. The study consisted of a twice daily application of material for 12 weeks followed by a 4-week regression phase. Stratum corneum lipids were collected and then exposed to 500 mJ/cm2 of ultraviolet B (UVB) radiation in order to avoid excessive erythemal damage to the subjects. Lipid peroxides were assayed by a methylene blue derivative assay and expressed per unit area of skin. During the treatment period, decreases in the level of lipid peroxides were observed on the sites treated with the compositions containing antioxidants, as compared to the untreated sites, and expressed as percent differences. Decreases were observed in endogenous as well as UV-induced lipid peroxides followed by a return to baseline levels. These results demonstrate that antioxidants in a topical cosmetic formulation were effective in protecting human stratum corneum lipids against endogenous oxidation or if challenged by 500 mJ/cm2 UVB.