Lipid ingredients in moisturizers can modulate skin responses to UV in barrier-disrupted human skin in vivo

BackgroundChemicals with a molecular weight <500 and adequate lipid solubility can penetrate the intact human skin. As many lipid ingredients in moisturizers have molecular weights <500, the lipid ingredients may penetrate into the skin and affect skin responses to UV; however, little is known about this phenomenon.ObjectiveTo evaluate the effects of major lipid ingredients in moisturizers on skin responses to UV in tape-stripped human skin in vivo.MethodsWe evaluated the effects of three major lipid ingredients in moisturizers (cholesterol, linoleic acid, and a synthetic ceramide, N-oleoyl-phytosphingosine) on skin responses to UV in the tape-stripped skin of healthy volunteers. After 2 days of lipid-application, the areas were irradiated with UV, and skin samples were obtained 24 h after irradiation. Histologic features and the expression of the markers of collagen metabolism and inflammatory mediators were evaluated.ResultsCompared to vehicle, topical cholesterol significantly decreased the degree of dermal inflammatory infiltrates and exocytosis, and also decreased the expression of MMP-1, IL-6, and IL-1ß mRNA. In contrast, topical linoleic acid increased the induction of apoptotic cells, and the expression of MMP-1 and IL-6 mRNA. N-oleoyl-phytosphingosine increased the expression of MMP-1 and IL-6 mRNA, while decreasing the expression of COX-2 mRNA.ConclusionsTopical cholesterol can protect the barrier-disrupted skin against UV-induced damage, while linoleic acid or N-oleoyl-phytosphingosine alone has the potential to aggravate the damage.