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J. Soc. Cosmet. Chem., 21,417-425 (May 27, 1970) Torsional Measurements on Skin* KARL LADEN, Ph.D.,* and ROBERT MORROW, M.S.* Synopsis--An apparatus is described for measuring the STIFFNESS and ELASTICITY of thin strips of SKIN. Physical properties of skin in TORSION show decreases in sliffness with increased humidity of the ambient environment. The elasticity of the strips under- went a minimum between 50-80% relative humidity. Extraction of naturally occurring humectant was demonstrated to increase the physical stiffness of CALI•US and the addition of a humectant such as SODIUM PYRROLIDONE CARBOXYLATE to the skin was shown to increase softness. INTRODUCTION Softness and elasticity of the stratum corneum arc two important physical properties that contribute to the normal function of the skin. Previous investigations (1-4) have reported in a qualitative way the role of water and natural moisturizing agents in maintaining the softness and flexilibity of stratum corneum. In an effort to obtain more precise data, an instrument was constructed to measure in a quantitative manncr the changes in skin softness and elasticity with varying treatments and changes in relative humidity. EXPERIMENTAL Large untreated plantar calluses were vapor hydrated by holding at 100% RH. The hydrated specimens were sectioned horizontally on a t•reezing stage microtome to 50 t• avoiding any contact with liquid water. These sections were, depending on the nature of the experiment, either left untreated or extensively extracted with diethyl ether and water. Study conducted at the Toni Co., Division of the Gillelte Co., Chicago, Ill. Gillette Research Institute, Inc., 1413 Research Blvd., Rockville, Md. 20850. Ben May Labs, University of Chicago, Chicago, Ill. 417