j. Cosmet. Sci.,54, 289-300 (May/June 2003) Effect of soaking and naturalmoisturizing factoron stratum corneum water-handling properties MARTY O. VISSCHER, GAURAV T. TOLIA, R. RANDALL WICKETT, and STEVEN B. HOATH, The Skin Sciences Institute (M. O.V., S.B.H.), Cincinnati Children's Hospital Medical Center (M.O.V., S.B.H.), and College of Pharmacy (G.T.T., R.R.W.), University of Cincinnati, Cincinnati, OH 45267. Accepted for publication June18, 2002. Presented asa poster at the Annual Scientific Seminar of the Society of Cosmetic Chemists, New Orleans, May 2001. Synopsis Stratum corneum (SC) hydration is partiallyregulated by water-soluble molecules, naturalmoisturizing factor (NMF) that is associated with the corneocytes. Routine waterexposure, e.g., bathing, may deplete NMF and alter the SC water-handling properties. We determined the effects of bathing and solvent extraction on the volarforearm skin of eleven healthy volunteers. Acetone/ether (A/E) was used to remove surface and upperSC lipids.Adjacent sites weresoaked for ten minutes or treated with the A/E-plus-soak combination. Subsequently, an NMF formulation was applied to the treated sites, andtransepidermal water loss (TEWL), hydration, and moisture accumulation rate (MAT) were measured. A/E extraction increased TEWL, but did not effect MAT. Soaking produced a short-term increase in TEWL, followed by a decrease, andsubstantially reduced MAT, aneffect that was maintained for fivehours. NMF application significantly decreased TEWL and significantly increased MAT for all sites. The replacement experiment suggests that the MAT reduction occurred as a result of extraction of hygroscopic NMF components. The effects of soaking and NMF application are morereadily detected by the MAT technique, whereas TEWL is more sensitive to A/E extraction. The results support the use of multipleassessments of barrier function andraise questions aboutthe effects of cumulative repeated waterexposure on SC function. INTRODUCTION The stratum corneum (SC)forms a dynamic interface between the environment and the internal milieu. Proper hydration of the SC is essential to provide an effective barrier to waterloss andfor optimumskinfunction (1). Plasticization of the SCimparts flexibility and prevents cracking, fissuring, barrier damage, andloss of integrity. SCmoisturization occurs as a result of the inherent barrier to water lossprovided by the corneocytes embedded in the lipid bilayer matrix andby the inherent humectancy of specific cellular components (2). Hydration is necessary for properdesquamation of the outer SC by facilitatingdegradation of desmosomal attachments (3). Topical moisturizers, usedto treat dry, scaly skin conditions, provide humectancy and water-holding capability with 289