OPPOSING EFFECTS OF GLYCEROL ON THE PROTECTIVE FUNCTION OF THE HORNY LAYER AGAINST IRRITANTS AND ON THE PENETRATION OF HEXYL NICOTINATE

Background: It is known that glycerol in an oil-in-water emulsion has a protective effect against irritating substances. Objective: To answe r the question: is the protection effect of glycerol based on a regene rative process? Methods: Upon irritation by either tape stripping or a cetone treatment, we applied glycerol to the skin surface under an occ lusive dressing to create transepidermal water movement. As a control we used water under the occlusive dressing on the contralateral forear m, 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 res istance and by the irritant effect of dimethyl sulfoxide (DMSO) as wel l 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.