CHANGES IN STRATUM CORNEUM 107 Cycloryl NA ©) were supplied by Alcolac, Inc. (Baltimore, MD). PEG-20 glyceryl monotallowate (Varonic LI-42 ©) was supplied by Sherex Chemical Company (Dublin, OH). All the surfactants were used as supplied to prepare the dilutions of test solutions for patch application. Deionized water was used as the diluent and was also used as the control. The same molar concentration of different surfactants was used throughout this study. The molar equivalent of 2% (w/v) SLS is 0.063 mole/liter based on the average molecular weight provided by the manufacturer. Thus, the test concentration of SLES was 2.9% (w/v) and of PEG-20 glyceryl monotallowate was 7.9% (w/v). EXPOSURE AND EVALUATION SCHEDULE For each application, 0.3 ml of surfactant solution was placed on the absorbent disc of a 25-mm diameter Hilltop Chamber ©. The Hilltop chamber was supplied affixed to a 2" x 2" square of adhesive tape. The chamber was applied to the volar aspect of the forearm about 40 mm above the wrist. A chamber containing deionized water without any surfactant was applied to the same area of the opposite forearm. The subjects were randomized as to which forearm was treated with surfactant and which forearm served as the control. The patch sites were marked with a permanent marking pen to facilitate positioning of the patches at the same site. Two applications, 45 minutes each, were made daily for five consecutive days. The time interval between these two applications was approximately four hours. After patch removal, the skin was cleansed with running water and gently dried with a cotton towel. At least 30 minutes elapsed before instrumental measurements and clinical observations were made following the second patch application on each day. TRANSEPIDERMAL WATER LOSS (TEWL) MEASUREMENTS TEWL measurements were performed with a single-probe Servo-Med © Evaporimeter EP-1C (Servo-Med, Stockholm, Sweden) (20,21). In order to avoid measurement errors caused by air currents and changes in relative humidity, TEWL measurements were performed in a custom-made chamber into which the subject placed the forearms. Dry air was flowed into the chamber during the acclimation period, if necessary, to provide RH between 45% to 50% in the chamber. After an acclimation period of approximately 30 minutes, the instrument's detection probe was applied perpendicularly to the skin area to be measured and allowed to equilibrate for 30 seconds. The internally computed TEWL value was then recorded. ELECTRICAL CONDUCTANCE MEASUREMENTS The Skicon-200 © hygrometer (I.B.S. Co., Ltd., Shiznoka-ken, Japan) was used to perform electrical conductance measurements. The spring-loaded probe was applied to the skin with a standard pressure of 30 grams. A detailed description of the measuring principle was published by Tagami and coworkers (22). Measurements of electrical conductance were made within the environmental chamber immediately after the TEWL measurement. Measurements were made in triplicate and the mean value was used.

108 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS INFRARED (IR) SPECTROSCOPIC MEASUREMENTS Attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopic measurements were performed with a Perkin-Elmer Model 1600 FTIR spectrophotom- eter (Perkin-Elmer Corporation, Norwalk, CT) with a side focus horizontal attachment and an internal reflection element (IRE) of zinc selenide (Harrick Scientific Corporation, Ossining, NY). The patched skin site was placed directly on the IRE. The applied pressure corresponded to the weight of the forearm, and was adjusted (if necessary) based on the reading of the intensity of the incident light through the prism. The amide I band (approximately 1,645 cm-•) and the amide II band (approximately 1,545 cm-•) were used to determine skin moisture. While the amide II band is only minimally altered by the presence of water, the amide I band is greatly affected. The absorption ratio of amide I to amide II bands was calculated and will be referred to as the moisture factor (MF). A detailed description of this technique was published by Puttnam (23). SKIN REFLECTIVE COLOR MEASUREMENTS Skin color and reflectance measurements were performed with a Minolta Chroma Meter ©, Model CR-200 (Minolta Camera Co., Ltd., Osaka, Japan). Absolute measure- ments were taken in L*a*b* (CIE 1976) system. The L* values indicated the brightness of the skin being analyzed, and the positive a* values (+ a*) the erythema of the skin surface. Bubulak et al. (24) described in detail the methodology of this measurement technique. ANALYSIS OF SKIN REPLICAS Negative skin replicas of each subject's test sites were made with Silflo © quick-drying silicone rubber (Flexico Developments Ltd, Potters Bar, England). For capturing the image onto a videodisc, a Zeiss OMP-1 Stereo operating microscope (Carl Zeiss, Inc., Thornwood, NY), a special Dage-MTI CCD-72 video camera (Dage-MTI, Inc., Mich- igan City, IN), and a Targa-M8 © frame grabber (Truevision, Inc., Indianapolis, IN) were used. Care was taken to preserve the orientation of the replicas with respect to the actual forearm skin to allow for accurate interpretation of day-to-day changes. The skin replica was taped onto a metal cassette, which was placed in a custom-made light-tight box to prevent stray light from striking the replica. The intensity of the light sources was strictly controlled by a highly regulated power supply. Fiberoptic light pipes were used to provide even illumination at an angle set at 20 ø incidence. Two images were captured from each replica by using two incident light sources set at right angles to each other. The image was visualized on a video monitor, and selected fields were stored on video floppy discs using a Canon Still Video Recorder (Canon, Inc., Tokyo, Japan). A 386-based microcomputer was used in conjunction with JAVA © video analysis software (Jandel Scientific, Corte Madera, CA) for all image processing, analysis, and control functions. The process for image analysis can be briefly summarized as follows: First, a 12-mm x 12-mm area from the middle of each image was defined as the area for analysis. The defined area was then divided into 512 x 512 pixels of 256 gray levels