INFRARED SPECTROSCOPY OF SKIN 87 (8) R. E. Baier, Noninvasive, rapid characterization of human skin chemistry in situ, J. Soc. Cosmet. Chem., 29, 283-306 (1978). (9) M. Gloor, U. Willebrandt, G. Thomer, and N. Kupferschmid, Water content of the horny layer and skin surface lipids, Arch. Dermatol. Res., 268, 221-223 (1980). (10) M. Gloor, G. Hirsch, and U. Willebrandt, On the use of infrared spectroscopy for the in vivo measurement of the water content of the horny layer after application of dermatologic ointments, Arch. Dermatol. Res., 271, 305-313 (1981). (11) M. Gloor, B. Heymann, and Th. Stuhlert, Infrared-spectroscopic determination of the water content of the horny layer in healthy subjects and in patients suffering from atopic dermatitis, Arch. Dermatol. Res., 271, 429-436 (1981). (12) A. Triebskorn, M. Gloor, and F. Greiner, Comparative investigations on the water content of the stratum corneum using different methods of measurements, Dermatologica, 167, 64-69 (1983).

j. Soc. Cosmet. Chem., 37, 89-97 (March/April 1986) Soap and detergent bar rinsability MITCHELL S. WORTZMAN, RICHARD A. SCOTT, and PETER S. WONG, Neutrogena Corporation, 5755 W. 96th Street, Los Angeles, CA 90045,' NICHOLAS J. LOWE and JAMES BREEDING, University of California, Los Angeles, School of Medicine, Department of Dermatology, Westwood, CA 90024. Received April 4, 1983. Presented at the SCC Scientific Seminar, Cincinnati, Ohio, May 5-6, 1983. Synopsis Studies on the role of cleansing bars in skin irritancy have focused on pH and composition. The rinsability factor is ignored by chamber style tests but seems to be significant in usage experience. In order to understand the differences seen in chamber and use testing, 18 common soap, combats, and syndet bars were studied for their rinsing characteristics, which were compared to their irritancy potential. The relative rinsabilities of the products were determined photographically and spectrophotometrically using soap solu- tions spiked with fluorescein dye. The dye-containing soap solutions were applied to the forearms of volunteers, worked into a lather, and rinsed uniformly. The residues were then either photographed or extracted from the skin and quantified spectrophotometrically. Both photographic aand spectroscopic methods demonstrated that there are significant differences in rinsabilities among the products tested. Deodorant bars, regardless of composition, rinsed poorly. Facial bars and "mild bars" tend to have superior finsabilities. INTRODUCTION The effects of soap products on skin have been the subject of continuous controversy and debate (1,5). The most popular form of personal soap product remains the original bar. Bar soap products can be divided into three types: Soap bars are mainly composed of the alkali salts of long chain fatty acids and have a pH between 9.0 and 10.0. Combats are composed primarily of alkaline soaps (pH 9.0 to 10.0) to which various surface active agents are added to act as lime soap dispersants (2). Syndet bars consist primarily of synthetic detergents and fillers which contain less the 10% soap and generally have an adjusted pH between 5.5 and 7.0 (2). A major point of differentiation between these three types has been their potential for skin irritation or mildness as it is commonly referred to. Until recently, the prevalent dermatologic thinking was split over the importance of the alkaline nature of soaps in cutaneous irritancy (4). The soap chamber test, developed by Kligman and Frosch, clearly demonstrated that pH in the range of 5.5 to 10.0 has little or no effect on the irritancy of soap or detergents (5). This result is probably due to the high buffering capacity of the skin. However, more recent work by Frosch in 89