Assessment of the water content of the stratum corneum using a sorption-desorption test

Background/Aim: Various instruments based on electrical properties of the s kin are currently used to assess the stratum corneum (SC) hydration state o r water holding capacity. However, no direct relation with the quantity of water measured is provided. The objective of the present study was to calib rate the Corneometer, a device displaying electrical-capacitance-related va lues (which reflect the skin hydration state), and the amount and behaviour of the water taken up by the outer part of the SC during a sorption-desorp tion test. Methods: The experiment was performed on the ventral forearms of 20 healthy volunteers after a rest in an environmentally controlled room. Corneometer and transepidermal water loss (TEWL) values were measured at in tervals over the desorption process. The areas under the TEWL-versus-time c urve provided the absolute amounts of residual sorbed water. Results: The d ecrease kinetics of both signals after subtraction of prehydration values w ere very similar and bi-exponential, both showing a rapid, then a slower ph ase. The absolute amount of water taken up by the SC (hygroscopicity) and t he two desorption rates were obtained. The Corneometer values were monoexpo nentially related to the amount of water remaining within the SC. This allo wed the in vivo calibration of the Corneometer in terms of absolute amount of water over the desorption range. Conclusion: The method may be used to c alibrate in vivo other electrical devices aimed at assessing SC hydration d uring a sorption-desorption test. It may also provide new ways to measure S C water uptake and water holding capacity following application of products . Copyright (C) 2001 S. Karger AG, Basel.