Cosmet. Sci., 52, 23-33 (January/February 2001) The ability of electrical measurements to predict skin moisturization. II. Correlation between one-hour measurements and IonD-term results 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. Synopsis We investigated the ability of short-term (one-hour) electrical measurements with three different commonly used instruments to predict the effects of long-term treatment with glycerin-containing formulations on moderately dry leg skin. We report the moisturizing effects of glycerin on healthy female adult skin in a two-week study as measured by electrical conductance and capacitance, transepidermal water loss (TEWL), and clinical grading of skin dryness. The test formulations contained 1.5% NaC1 and levels of glycerin from 0% to 15 %. Results obtained with a smaller cohort of ten subjects, one hour after treatment, were predictive of moisturizing efficacy in the two-week period among twenty subjects with dry leg skin. Our results show that single application tests can be predictive of longer-term results with humectant-based moisturizers and that electrical measurements of skin conditions correlate well with skin grades. INTRODUCTION Use of non-invasive electrical instruments to determine skin hydration has become widely accepted (1-4). The reliability of commercial instruments for electrical measure- ments and the correlation of these methods with each other have been investigated (5,6). Bart eta/. (16) found that long-term application of glycerin resulted in improved skin condition as measured by reduced electrical impedance, reduced transepidermal water loss, increased coefficient of friction, increased skin smoothness. They explained the phenomenon by assuming that glycerol interacts with stratum comeurn lipid structures or proteins, altering their water-binding and/or hydrophilic properties, and therefore changing the status of water in the outer layers of the SC. In Part I of this study, we showed a strong linear relationship with electrical response and glycerin concentration in a two-hour, single-application test using three different commercial instruments. We also reported that salt in the formulation can significantly affect the electrical device readings and that the salt effect is dependent on glycerin concentration. 23

24 JOURNAL OF COSMETIC SCIENCE In this work, we studied the moisturizing effect of glycerin on healthy female dry leg skin in a two-week study by using both non-invasive measurements and clinical grading. Measured parameters include electrical conductance and capacitance, transepidermal water loss (TEWL), and expert skin dryness grades. The primary objective of this study was to determine whether short-term electrical measurements can be predictive of long-term skin moisturization. A constant amount of sodium chloride was added to each formulation to incorporate the effects of salt on instrumental readings and/or skin effects. We also investigated the correlation between instrumental measurements and skin grades. MATERIALS AND METHODS ELECTRICAL MEASUREMENTS The Corneometer © CM 825 (Courage-Khazaka Electronic, Cologne, Germany) measures skin hydration by determination of skin capacitance and operates at a mean frequency of 1 MHz (1.15 MHz, very dry medium 0.95 MHz, very hydrated medium). The mea- surements are provided in arbitrary units (AU) ranging from 0 to 120 AU (5-7). The Skicon © 200 (lBS Company, Hamamatsu, Japan) measures conductance at a fixed cur- rent of 3.5 MHz. The measurement values are provided in micro-siemens (ps) units, ranging from 0 to 1999 ps (5,6,8). The Nova © Dermal Phase Meter 9003 (NOVA Technology Corporation, Portsmouth, NH) is a capacitance instrument. Measurement values are obtained by integrating measurements at different frequencies of the applied alternating current at preselected variable frequencies up to 1 MHz. The final readout is given in arbitrary DPM units (AU), ranging from 90-999 (5,6,9). TRANSEPIDERMAL WATER LOSS The single-probe DermaLab © evaporimeter (Cortex Technology, Hadsund, Denmark) with cyberDERM software (Media, PA) measures transepidermal water loss (10,11). This device is connected to a computer and automatically reports the average of the readings after the probe is in contact with the skin for 30 seconds. The principle of this device has been described in detail (12,13). FORMULATIONS Four formulations were used in the study, with glycerin concentrations of 0%, 5%, 10%, and 15%, respectively. The components of the oil phase were mineral oil (3.0%), cetyl stearyl alcohol (1.5%), stereth-2 (1.5%) and stereth-20 (2.5%). The water phase con- tained hydroxyethylcellulose (thickener, 0.5%), Germaben II (preservative, 0.1%), and sodium chloride (1.5%). SUBJECTS A group of twenty healthy female subjects between 18 and 57 years of age participated in a two-week treatment phase. A second and separate group of ten subjects were