About the effects of Ethanol on skin – Reduction in hydrophilic penetration

Microbiological stability poses a significant challenge in the manufacturing of fluid and semi-solid formulations intended for topical application. One of the most effective strategies to address this issue is the incorporation of preservative substances. Ethanol is one of the most widely used natural preservatives in cosmetics.

This study examined the effects of ethanol in a semi-solid formulation on the dermal penetration efficacy of a hydrophilic model drug. Dermal penetration was evaluated using the Marburg ex vivo porcine ear skin model on both intact and irritated skin.

The results demonstrated that dermal penetration was about 46% lower in irritated skin compared to intact skin. Ethanol reduced the dermal penetration efficacy by nearly 40% for intact skin and by approximately 5% for irritated skin. These observations may be attributed to the formation of a “pudding skin,” where the upper layer of the skin becomes dehydrated, resulting in increased density and decreased permeability for the model drug. In intact skin, ethanol contributes to the formation of the pudding skin. For irritated skin, with its impaired barrier, the formation of a pudding skin occurs as the skin dries out. Consequently, the additional ethanol led to only a slight increase in skin dryness, resulting in only a minor decrease in the penetration efficacy of the hydrophilic model drug.
In conclusion, if the skin dries out on the surface, a 'pudding skin' forms, which reduces the penetration of hydrophilic active ingredients.