Effects of water activity and low molecular weight humectants on skin permeability and hydration dynamics – a double‐blind, randomized and controlled study

Abstract

Synopsis Objectives The mammalian skin is a barrier that effectively separates the water‐rich interior of the body from the normally dryer exterior. Changes in the external conditions, for example ambient humidity, have been shown to affect the skin barrier properties. The prime objective of this study was to evaluate the effect of water activity of a topical formulation on skin hydration and permeability. A second objective was to gain more understanding on how two commonly used humectants, urea and glycerol, affect skin barrier function in vivo. Methods Simple aqueous formulations were applied under occlusion to the volar forearm of healthy volunteers. Following 4‐h exposure, skin water loss (by transepidermal water loss measurements), skin hydration (by Corneometry) and skin permeability (by time to vasodilation due to benzyl nicotinate exposure) were monitored. Results The results demonstrate that a relatively small change in the water activity of a topical formulation is sufficient to induce considerable effects on stratum corneum hydration and permeability to exogenous substances. Exposing the skin to high water activity leads to increased skin hydration and also increased permeability. Furthermore, urea and glycerol promote skin hydration and permeability even at reduced water activity of the applied formulation. Conclusion These results highlight the importance of considering the water activity in topically applied formulations and the potential benefit of using humectants. The results may impact formulation optimization in how to facilitate skin hydration and to modify skin permeability by temporarily open and close the skin barrier.

Glyceryl Ether (mono-tert-butoxypropanediol) in Emulsion System

“…Even though the moisturizing property of glyceryl ether is lower than glycerol, it still exhibits a good moisturizing effect to skin. A high skin hydration level of emulsion containing glycerol was reported by Alber et al (2014). The superior moisturizing property of glycerol could be attributed to the three hydroxyl groups in the glycerol molecule, whereas the glyceryl ether has only two hydroxyl groups.…”

Exploring the potential for rosacea therapeutics of siRNA dispersion in topical emulsions

“…The observed interphasic localization of the RNA in the emulsion suggests a surfactant effect, presumably effect of multiple interactions with the functional groups of the components in the emulsion (Figure ) . Mechanisms for urea‐dependent skin permeability enhancement were previously discussed; for example, in the works Albèr et al and Björklund et al described the enhancement of skin permeability mediated by urea, as effect of ultrastructural changes . Furthermore, Jatana et al suggested that commonly used active ingredients, such as urea and glycerol, could highly affect the skin penetration of particulates, and thus, it could possibly results in the cutaneous deposition of water‐soluble macromolecules up to a size of few nanometres .…”

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“…Several studies have demonstrated that glycerine promotes skin hydration and can also increase skin permeability [45][46][47][48].…”