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J. Soc. Cos,Tctic Che,•isls, 19, 841-847 (Dec. 9, 1968) The Effect of Dimethyl Sulfoxide on Percutaneous Absorption: A Mechanistic Study, Part III STANLEY G. ELFBAUM, Ph.D., and KARL LADEN, Ph.D.* Presented April 21-23, 1968, Washington, D. C. Synopsis--Additional studies have been carried out to support the suggested swelling role of dimethyl sulfoxide (DMSO) toward hair fibers. Results again indicate that large con- centrations of solvent are required before appreciable swelling and greater uptake of DMSO can be realized. The swelling process is easily reversible. Other data indicate that DMSO at low pH values may be responsible for an increase in eoulombie repulsions within the fiber which results in greater swelling. With the more complex substrate, skin, the modifying role of DMSO on the skin barrier is more difficult to assign. The DMSO effect has not been shown to be reversible and results indicate that lipid extraction may play a supporting role to protein swelling in this modification process. INTRODUCTION In two previous papers, the effects of dimethyl sulfoxide (DMSO) upon the in vitro percutaneous absorption of picrate ion through excised guinea pig skin and upon some physical properties of several proteins have been reported (1, 2). As a result of studies on bovine serum albu- min, •-lactoglobulin, and hair keratin, DMSO was considered to be a pro- tein swelling agent. With a complex substrate such as skin, the role of DMSO is more difficult to assign and further experiments were proposed. The results of these studies are presented in this paper. * Gillette Research Institute, 1413 Research Boulevard, Rockville, Md. 20850. 841