The human stratum corneum is exposed permanently to solar ultraviolet light. UV radiation is able to induce lipid peroxidation. In the presented study, liposomes prepared from human stratum corneum lipids as well as from synthetic lipid mixtures were exposed to UV radiation. The UV-induced oxidation was followed by quantification of lipid oxidation products (malondialdehyde and lipid hydroperoxides) as well as by the oxygen consumption. High cholesterol concentrations in the vesicle membranes led to an increased formation of lipid hydroperoxides. In addition, the malondialdehyde generation was decreased. However, the total oxygen consumption during the UV irradiation was not influenced by the cholesterol concentration. A possible antioxidative effect of cholesterol is discussed. To clarify the mechanism of oxidation, cholesterol oxidation products were analyzed by high-performance thin-layer chromatography. The appearance of 7a- and 7b-hydroxy-cholesterol indicated the type I oxidation mechanism, in which oxygen radicals appear as intermediates. Finally, liposomes were exposed to natural solar light. A similar relationship between malondialdehyde and lipid hydroperoxide formation was observed. The oxidation mechanism was identified as type I, too.