PHOTOSTABILITY OF UV FILTERS 11 Evaluation of in vitro percutaneous absorption of UV filters used in sunscreen formulations, Drug Cosmet. Ind., 50-62 (May 1996). (17) G. Potard, C. Laugel, A. Baillet, H. Scaefer, and J.P. Marty, Quantitative HPLC analysis of sunscreen and caffeine during in vitro percutaneous penetration studies, Int. J. Pharm., 189, 249-260 (1999). (18) P. Treffel and B. Gabard, Skin penetration and sun protection factor of ultra-violet filters from two vehicles, Pharmaceut. Res., 13, 770-774 (1996). (19) G. Yener, J. Hadgraft, and W. John Pugh, Penetration of two sunscreens in various formulations through a synthetic membrane as compared to human skin in vitro, Acta Pharmaceut. Turcica, 1, 27-32 (1998).

j. Cosmet. sci., 52, 13-22 (January/February 2001) The ability of electrical measurements to predict skin moisturization. I. Effects of NaCl and glycerin on short-term measurements FANG LI, EILEEN CONROY, MARTY VISSCHER, and R. RANDALL WICKETT, College of Pharmacy, University of Cincinnati (F.L., E.C., R.R.W.), and The Skin Sciences Institute, Children's Hospital Medical Center (M. V.), Cincinnati, OH 45267. Accepted for publication January 15, 2001. Presented as a poster at the Annual Scientific Seminar of the Society of Cosmetic Chemists, Chicago, May 6-7, 1999. Synopsis Non-invasive methods to evaluate skin hydration by measuring electrical properties are widely used in the cosmetic industry. However, there is still some controversy about factors that affect measurement. For example, concerns have often been expressed about the possible confounding effect of salts, either in the formulation or on the skin. Ionized salts on the skin may increase electrical conductivity and may lead to changes in electrical properties that are not related to increased water content. We have performed a systematic study of the effects of salt, i.e., sodium chloride, and glycerin on the electrical properties of skin as measured by the three most commonly used instruments, the Nova © DPM 9003, the Corneometer © CM 825, and the Skicon © 200. Formulations containing salt from 0-3% and glycerin from 0-] 0% were tested for their effects at one and two hours after a single application. Salt lowered the readings in the absence of glycerin and increased the reading in the presence of glycerin. For all three instruments, there was a linear correlation between the measurement and the glycerin level in the presence or absence of salt. INTRODUCTION The term dry skin refers to skin features that give an impression of dryness, roughness, scaling, fissures, and cracks (1). Dry skin develops because of decreased water content in the horny layer (2,3). More recently, Warner and Lily have shown conclusively that dry skin lacks water (4). Moisturizing lotions are widely used to hydrate the skin surface and relieve the symptoms of dry skin. Evaluating the efficacy of these products constitutes an important task, especially in the course of substantiating the moisturizing claims of cosmetic products. In recent years, non-invasive methods to evaluate, quantify, and compare skin hydration by measuring electrical properties have become increasingly popular (5). Commercially available instruments, based on principles of measuring skin capacitance, conductance, or impedance (3,5-8), are becoming mature and have been widely used for this purpose. There is ample evidence that these measurements do 13