I. Soc. Cosmetic Chemists, 21, 129-140 (Feb. 4, 1970) Effect of Dimethyl Sulfoxide and Other Reagents upon Mechanical Properties of Stratum Corneum Strips STANLEY G. ELFBAUM, Ph.D., and MARIA A. WOLFRAM, Ph.D.* Presented May 8, 1969, New York City Synopsis--The mechanical properties of guinea pig stratum comeurn strips exposed to DIMETHYL SULFOXIDE (DMSO) and several other reagents have been examined. With DMSO concentrations greater than 50% and after a 24-hour incubation period, a marked reversible strengthening of the S•4•N strips relative to their behavior in water was noted. This observation correlates well with other experiments and reports which indicated that the DMSO swelling of skin and hair is accompanicd by a stiffening effect. To further elucidate thc proteinaceous nature of the skin barrier, several other reagents were cxamined for their effects upon the strength of stratum comeurn strips. A known cystine bond reducing agent (ammonium thioglycolate) and protein denaturating agents (urea and formic acid) considerably weakened guinea pig stratum corneum. The cross- linking ability of formaldehyde was revealed in its strengthening effect upon skin strips. Trichloroacetic acid (a protein precipitant) and phenol behaved in a similar manner. The reversibility of the mechanical effccts caused by these various reagents has been studied and thc results are presentcd. INTRODUCTION Previous reports from this laboratory have shown that dimethyl sulfoxide (DMSO) is capable of swelling and unfolding several soluble proteins (1). Other laboratories have demonstrated a swelling of wool fibers caused by large concentrations of DMSO (2, 3). Hair keratin undergoes a similar swelling effect which occurs in a reversible manner (1, 4, 5). However, it is of interest that the mechanical properties of hair Gillette Research Institute, Inc., 1413 Research Blvd., Rockville, Md. 20850. 129

130 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS appreciably swollen in large concentrations of DMSO indicate that the fibers appear stronger than in H20 even though they have undergone ex- tensive swelling (6). With skin, the penetrating ability of DMSO has been well docu- mented (7-12). One is tempted to envision this effect in part as an open- ing up or swelling of the proteinaceous components o[ the stratum cor- neum matrix. Indeed, wrinkling and turgid effects have been observed both on the fingers and palms of laboratory personnel and patients who came into contact with DMSO and on whole guinea pig skin membranes which had been exposed to large concentrations of DMSO (1, 8, 9). Although the swelling characteristics of hair in DMSO and the DMSO-enhanced passage of materials through whole skin show a similar dependence upon DMSO concentration, the two processes may not be completely alike. The nonreversibility of the in vitro DMSO-enhanced diffusion of pictate ion through whole intact skin indicates lipid extrac- tion or irreversible protein denaturation may have played supporting roles in the solvent initiated modification of the skin barrier (4). Since chemical effects upon stratum comeurn and the resulting physical responses are relatively unknown, a study of the effect of DMSO and several other reagents on the mechanical properties of isolated strips of stratum comeurn has been undertaken. It was hoped that this ap- proach would provide more insight concerning the proteinaceous nature of the stratum comeurn, especially since the physical or mechanical re- sponses of tissue strips to chemical reagents reflect in part different degrees of solvation, hydration, and protein denaturation (13). EXPERIMENTAL Materials Analytical grade reagents and solvents were used without further purification. Ammonium thioglycolate (0.1M) was prepared by adjusting 0.1M thioglycolic acid to pH 9 with concentrated ammonia solution. Ammonium chloride (0.1M) was adjusted to pH 9 with concen- trated ammonia solution. Guinea pig stratum comeurn was isolated by exposing excised in- tact skin to ammonia vapors and then gently peeling off the stratum cor- neum (14). The sheets of stratum corneum were stored at --12øC. Strips of human stratum corneum were obtained from sunburn peel- ings.