Opposing Effects of Glycerol on the Protective Function of the Horny Layer against Irritants and on the Penetration of Hexyl Nicotinate

Abstract

Background: It is known that glycerol in an oil-in-water emulsion has a protective effect against irritating substances. Objective: To answer the question: is the protection effect of glycerol based on a regenerative process? Methods: Upon irritation by either tape stripping or acetone treatment, we applied glycerol to the skin surface under an occlusive dressing to create transepidermal water movement. As a control we used water under the occlusive dressing on the contralateral forearm. After 5 h we compared the barrier function using biological tests. Results: A significant improvement of the protective barrier function was observed in the glycerol-treated areas, as shown by the alkali resistance and by the irritant effect of dimethyl sulfoxide (DMSO) as well as sodium lauryl sulfate. Surprisingly, at the same time penetration of hexyl nicotinate improved on the glycerol-treated areas. A direct physicochemical protection effect on the surface of the skin was ruled out in additional studies using NaOH and DMSO. Conclusions: Under the given conditions glycerol leads to a more rapid reconstitution of the protective skin barrier and initiates a regenerative skin protection. In contrast to that, it is acting as a penetration enhancer.