beta-Carotene is widely used in skin care therapy. Its effects on skin are unclear, but actions on lipid peroxidation pathways may be an important element of any protection activities it exerts. This study examines the possible effects of Beta-carotene on enzymatic lipid peroxidation by lipoxygenase in human skin, using in vitro and ex vivo models. The effect of Beta-carotene on lipid peroxidation in human skin were studied in skin homogenates and in a semi-in vivo model of skin penetration, using [1-14C]-arachidonic acid or [1-14C]-linoleic acid as substrate. When relatively low concentrations (about 0.3 microM) of beta-carotene were added to epidermal homogenates, the major metabolites of arachidonic acid (12-hydroxy-cis-5,8,14, trans-10-eicosatetraenoic acid and 15-hydroxy-cis-5,8,11, trans-13-eicosatetraenoic acid) and of linoleic acid (13-hydroxy-cis-9, trans-11-octadeca dienoic acid and 9-hydroxy-trans-10, cis-12-octadeca dienoic acid) were significantly decreased. Following [1-14C]-linoleic acid penetration through the semi in vivo model layers, the skin surface was the main site in which the major linoleate product, 13-hydroxy-cis-9, trans-11-octadeca dienoic acid was detected. Furthermore, its level was inhibited by up to 80%, compared with the control, when beta-carotene was added to the system. The data presented in this study suggest possible interactions between beta-carotene and human epidermal lipoxygenase. Beta-carotene may effect lipid peroxidation in human skin, either as a free radical scavenger or as a specific lipoxygenase inhibitor.