Research Summary
Glycerin is widely used in cosmetics as well as in pharmaceutical formulations, primarily as a humectant. In vitro studies have shown that glycerin prevents crystallization of the stratum corneum model lipid mixture at low room humidity. However, it is unclear whether this effect might influence skin barrier function during repeated application of glycerin in a cream base to normal skin. Therefore, the influence of a cream containing 20% glycerin was compared with its placebo cream in a bilateral, double-blind study involving 17 healthy volunteers.
The effect was evaluated by measuring hydration with a corneometer and assessing skin barrier function. Skin barrier function was analyzed by its permeability to water using an evaporimeter (trans-epidermal water loss: TEWL) and by its sensitivity to an irritating surfactant by measuring the biological response in terms of TEWL and skin blood flow.
After 10 days of treatment on normal skin with 20% glycerin, corneometer values significantly increased, indicating improved hydration. However, the study did not show any influence of glycerin on human skin in terms of TEWL and skin sensitivity to sodium lauryl sulphate (SLS)-induced irritation.
The same findings were confirmed in a French study where a cream containing 20% glycerin was tested against a placebo cream in a bilateral, double-blind study on 17 healthy volunteers. The moisturizing effect of glycerin was evaluated using a corneometer, and its influence on skin barrier function was assessed using an evaporimeter (measuring trans-epidermal water loss) and its protective effect against irritation was tested using a surfactant agent by measuring biological skin responses (TEWL and blood flow).
After 10 days of treatment with a 20% glycerin cream, corneometer measurements showed a significant increase, indicating enhanced skin hydration. However, the study was unable to demonstrate any effect of glycerin on TEWL or its potential to reduce the irritant effects of sodium lauryl sulphate.
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