Equilibrium Water Content in Native Vernix and Its Cellular Component

Vernix caseosa is a naturally occurring substance coating the skin of newborn humans. Structurally, vernix contains fetal corneocytes embedded in a hydrophobic lipid matrix. Despite a relatively high water content approximating 80.7%, vernix exhibits slow water release. In this study, we quantified and contrasted the water release and uptake properties of native vernix and its isolated cellular component over the full range of water activity. Theoretical water sorption models (D'Arcy-Watt, and Frenkel-Halsey-Hill (FHH), and Guggenheim-Anderson-de Boer (GAB)) were fit to the vernix water sorption data. Each of the theoretical models provided a satisfactory description of the equilibrium water content of vernix over the water activity range 0.15-1.0. Vernix corneocytes without the surrounding lipid matrix exhibited markedly increased equilibrium water binding at water activities greater than 0.62 compared to native vernix. Resorption experiments showed full recovery of water content in both native vernix and isolated corneocytes supporting a structured internal domain. These results provide the first quantitative characterization of the water handling properties of native vernix and its cellular component. Such information may prove useful in the design of alternative skin care moisturizing formulations. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:985-994, 2008