The Mechanism of Moisturization by Glycerin and Propylene Glycol: Their Effects on the Intercorneocyte Lipid and Desmosome

Hwang, Sang Min; Park, Sang Hoon; Ahn, Sung Ku; Lee, Seung Hun

Abstract

BACKGROUND
Moisturizers induce skin hydration and then increase flexibility and elasticity, making the skin soft and smooth, and protecting it against environmental stimuli.
OBJECTIVE
The aim of this work was to study the role of intercorneocyte lipid layers and desmosomes in the mechanism of moisturization.
METHODS
Transepidermal water loss (TEWL) and capacitance were measured and the morphologic changes of the intercorneocyte lipid layers and desmosomes with electron microscopy, using ruthenium tetroxide (RuO4) postfixation, following the application of glycerin, propylene glycol, and a mixture of glycerin and propylene glycol for a 2 hour period to the epidermis of hairless mice were measured.
RESULTS
1. The TEWL was significantly increased in all three groups; glycerin, propylene glycol, and mixture of glycerin and propylene glycol. The increase of TEWL after the application of glycerin was maintained from the second to the forth hour after application which was statistically significant, after the application of propylene glycol it was maintained for 5 hours, and after the application of a mixture of glycerin and propylene glycol, for 6 hours. 2. The capacitance also was increased in all three experimental groups, compared to the control group. However there was no statistical significance. 3. Light microscopic findings showed no specific changes in all three groups, compared to the control group. 4. Ultrastructural observation by electron microscope, using RuO4 postfixation, showed widening of the intercorneocyte lipid layers in all three groups. In contrast to glycerin in which the results showed detachment of the desmosomes without changes in the intercorneocyte lipid layers, propylene glycol showed interruption and undulation of the intercorneocyte lipid layers and expansion of the lacunae spaces. A mixture of glycerin and propylene glycol showed interruption and undulation of the intercorneocyte lipid layers, detachment of the desmosomes, and, partial, formation of lacunae.
CONCLUSION
These results suggest that the moisturizing effects of glycerin result from an increased detachment of the desmosomes and widening of the intercorneocyte lipid layers and then an increase in the water holding capacity of the stratum corneum. Propylene glycol, a chemical penetration enhancer, induce widening, interruption, and undulation of the lipid layers and expansion of the lacunae space. In the mixture of glycerin and propylene glycol, propylene glycol potentiate and continue the moisturizing effects of the glycerin.