]. Soc. Cosmet. Chern., 23, 139-152 (March 3, 1972) The Absorption and Desorption of Cosmetic Chemicals on Skin ERIC JUNGERMANN, Ph.D., and H. C. SILBERMAN, Ph.D.* Presented May 24, 1971, Seminar, Washington, D.C. Synopsis--Stratum corneum in the form of excised CALLUS was used to measure the effect of xarious aqueous solutions on SKIN. Pieces of callus were immersed in distilled WATER, in ORGANIC SOLVENTS, and in aqueous solutions of DETERGENTS, HUMECTANTS, and SOAPS for different lengths of time. The weight increases were compared with the increases obtained by water alone. Repetitive soaking of callus in the same solution, al- ternating with air-drying, was investigated. The results allow a discussion of the factors which influence the water content of skin and the conservation of this water. INTRODUCTION It is well known that skin from various locations on the human body has different properties. Also, skin from different individuals be- haves quite distinctly (1). Striking data to this effect can be found in a publication by Marzulli (2), who measured the resistance of penetration by different areas of human skin. He found that steady-state penetra- tion rates were remarkably consistent for each tissue specimen. How- ever, biological variations were quite considerable thus, for the same location on the body, the penetration rates would vary by as much as a factor of 100. In previous publications, we have reported on the effect of presoak- ing with various surfactant solutions on the skin-water contact angle (3, 4). It was found that various cationic surfactants and amine oxides lowered the skin-water contact angle at the lowest concentration. Rinsability data supported findings and suggested that cationic surfactants are tightly bound to the skin. *Armour-Dial, Inc., Chicago, Ill. 60680. 139

140 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The present paper adds to our general knowledge of the properties of human skin with regard to permeability, substantivity, and softening under experimentally controlled circumstances. The methodology is described and results obtained with distilled water, organic solvents, detergents, soaps, and humectants are discussed. Characteristics of Callus Calluses occur on the soles or edges ot5 the 15eet where there is exces- sive friction. An acute excess will produce a blister, while chronic 15fic- tion produces a callus. Clinical inspection shows no special structural changes, only hyperkeratosis (5). The cellular stratification of the epi- dermis is simply a reflection o15 the various stages through which basal cells o15 the stratum germinativum pass in their gradual conversion into the horny material o15 the stratum corneum (6). Callus samples from different human donors behave very differently from one sample to another. This fact has influenced the methodology o15 our investigation to the extent that each experiment was performed jointly on one hal15 o15 a callus piece with the other hal15 as a control experiment. METHODOLOGY Calluses o15 approximately equal size (about 7 mm '•) were cut in half. One haft was weighed and immersed in distilled water, the other half was weighed and immersed in the experimental solution. In all subse- quent operations, such as removal from solution and weighing, both the control and the experimental sample were handled the same way and in close succession. This procedure greatly reduced the experimental error due to differences in exposure lengths and to fluctuations in ambient relative moisture content. The method was adopted because we were interested in measurable changes in the region o15 low relative humidity. Results by Blank (7) and Singer and Vinson (8) indicate that there is little fluctuation in moisture uptake o15 stratum corneum in the region of around 20% RH when the relative humidity changes a 15ew per cent our measurements were thus taken at 20% RH and 22øC. EXPERIMENTAL AND RESULTS Uptake and Release of Water by Callus Irnrnersed in Distilled Water Calluses were immersed in distilled water 15or different lengths of time. The water uptake was determined within 5 min a15ter the sample