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j. Soc. Cosmet. Chem., 34, 383-393 (November 1983) Electrometric technique for the in vivo assessment of skin dryness and the effect of chronic treatment with a lotion on the water barrier function of dry skin G. P. SERBAN, S. M. HENRY, V. F. COTTY, G. L. COHEN, and J. A. RIVELEY, Research and Development Laboratories, Bristol-Myers Products, 1350 Liberty Avenue, Hillside, NJ 07207. Received August 1, 1983. Presented at the Third International Symposium on Bioengineering and the Skin, Philadelphia, July 23, 1981. Synopsis Changes in skin capacitance induced by occlusion with a film of anhydrous petrolatum were measured with the aid of a pressure insensitive dry electrode on the forearms of 27 healthy volunteers, most of whom showed signs of superficial skin dryness. In subjects with dry skin the rate of increase in capacitance, which has been determined to signify diffusion of water to the surface of stratum corneum, was higher than in subjects with skin lacking manifestations of dryness. These results appear to support the concept that dry skin has a diminished ability to retain water. The difference could also be explained based on topographical characteristics and the presence of scales in dry skin. Chronic treatment with an ordinary skin lotion rendered dry skin normal-like with respect to its water barrier function. The technique presented here may have wider applications for testing the functional integrity of stratum corneum in vivo. INTRODUCTION In previous experiments (1) we observed that electrical measurements taken with a dry metal probe before and after occlusion with anhydrous white petrolatum were useful for analyzing the nature of changes in skin hydration induced by a brief solvent exposure. Solvent treatment caused (a) an increase in skin impedance signifying dryness, and (b) after occlusion, a decrease in impedance at a rate faster than that in untreated skin. Both effects would be expected if the solvent reduced the ability of the most superficial layers of the stratum corneum to retain water. A lowering in skin impedance after treatment with petrolatum has been reported by others (2,3), and it is attributed to the known properties of this material to hydrate the skin by reducing transepidermal water loss (4). Based on these facts, we inferred that the effect described in (b) above reflected the rate at which water from insensible perspiration reached and hydrated the surface of stratum corneum. In dry skin this rate is expected to be higher 383