A new computer-based evaporimeter system for rapid and precise measurements of water diffusion through stratum corneum in vitro

It is important to have reliable methods for evaluation of skin barrier fun ction when questions such as barrier perturbing effects of different agents and occlusive effects of different formulations are to be elucidated. A we alth of clinical work relates to measurements of transepidermal water loss in vivo, a method much affected by ambient air relative humidity, temperatu re, skin irritation processes, psychologic status of the subject, etc., fac tors that cause the method to suffer from low precision (i.e., high random error), Relating to these obstacles, we hare developed a closed ist vitro s ystem for measurements of water diffusion rate through pieces of isolated s tratum corneum at steady-state conditions, where the relative humidity and temperature is held constant and data can be collected continuously. Our ev aporimeter-based its vitro system has a more than 3-fold higher precision ( lower random error) (approximate to 10%) than measurements of transepiderma l water loss its vivo (approximate to 35%), The results of our study show t hat: (i) the corneocyte envelopes contribute to the barrier capacity of str atum corneum; (ii) removal of the lipid intercellular matrix results in app roximately a 3-fold increase in the water diffusion rate through the isolat ed stratum corneum (n = 20; p < 0.05), not a 100-fold as has previously bee n suggested; (iii) exposure to sodium dodecyl sulfate in water does neither alter the water diffusion rate (n = 10; p > 0.05) nor the water holding ca pacity (n = 10; p > 0.05) of stratum corneum; (iv) exposure to 1 M CaCl2 in water yields an increased water diffusion rate through stratum corneum (n = 10; p < 0.05); and (v) when applied to the stratum corneum in excess conc entrations, the penetration enhancer Atone has occlusive effects on water d iffusion through the stratum corneum (n = 6; p < 0.05).