Effects of ultraviolet A and B on the skin barrier: a functional, electron microscopic and lipid biochemical study.

To investigate the effects of ultraviolet A (UVA) and B (UVB) on the skin barrier, functional, electron microscopic and lipid biochemical studies were performed on normal and UV-irradiated skin of volunteers. Skin reactivity against primary irritants was evaluated using the alkali resistance test, the dimethylsulfoxide test and the sodium lauryl sulfate test. In all 3 irritation models, UVA- and UVB-irradiated areas were more resistant to damage than normal skin, indicating improvement of the barrier function after UV irradiation. In a second series of experiments, biopsies were taken and processed for electron microscopic evaluation of the stratum corneum. UVB significantly increased the horny cell layers; UVA did not alter the thickness of the stratum corneum. Finally, stratum corneum lipids were extracted in vivo and quantified after high-performance thin-layer chromatography. UVB and, to some extent, UVA exposure increased the amount of all stratum corneum lipids. This was also observed in all major ceramide subfractions.