846 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS CONCLUSIONS Equilibrium retention studies on hair fibers have suggested that DMSO is capable of swelling or unfolding proteins. The ease with which reversal of fiber swelling can be attained adds additional support to the swelling role of DMSO in these cases, as do viscosity studies on bovine serum albumin and •-lactoglobulin. In addition, Price and Menefee (6), in a recent paper, have presented the following suggestions, based upon stress relaxation measurements: (a) Large concentrations of DMSO interact reversibly with hair keratin through an initial dehydration effect which is accompanied by a swelling effect, a lowering of the modulus, and a promotion of disulfide interchange. (b) The relaxation rates of hair fibers incubated in concentrations of DMSO lower than 80% remain essentially unchanged from the rate observed in H20. Large concentrations of DMSO are required for appreciable effects to be observed. This concentration dependence is in agreement with the work of others (7) and work reported by the authors of this paper (1, 2). (c) The effect of DMSO upon hair keratin may also be similar to its effect upon increasing percutaneous absorption through the Stratum corneum. Although the swdling characteristics of hair and the passage of picrate through skin show a similar dependency upon solvent concentra- tion (1, 2), the two processes do not appear to be completely alike. Reversibility studies on diffusion through skin indicate that lipid ex- tractions may be playing a supporting role in the solvent initiated modifi- cation of the skin barrier. The lipid role in skin barriers has not been accurately defined (8) and it now appears that DMSO alters the skin barrier through some combination of protein swelling and lipid extrac- tion. It is of interest to note that chloroform-methanol solutions which are capable of both lipid extraction and irreversible protein denaturation within the skin barrier produce a much greater alteration than DMSO under similar conditions (9). ACKNOWLEDGMENTS The authors wish to thank Martha Yourshaw English for her tech- nical assistance with these studies. Thanks are also due Dorothy McCullen for her help in preparing this manuscript. (Received April 21, 1968)

DIMETHYL SULFOXIDE 847 REFERENCES (1) Elfbaum, S. G., and Laden, K., Mechanism of action of dimethyl sulfoxide: Part I, J. Soc. Cosmetic Chemists, 19,119-27 (1968). (2) Elfbaum, S. G., and Laden, K., Mechanism of action of dimethyl sulfoxide: Part II, Ibid., 19,163-72 (1968). (3) Van Holde, K. E., and Sun, S. F., Bovine serum albumin in watcr-dioxane mixtures, J. Am. Chem. Soc., 84, 66-72 (1962). (4) Stougton, R. B., Dimcthylsulfoxidc (DMSO) induction of astcroid reservoir in human skin, Arch. Dermatol., 91,657-60 (June 1965). (5) Stoughton, R. B., Hcxachlorophcnc deposition in human Stratum comeurn, Ibid., 94, 646-8 (Nov. 1966). (6) Price, V. H., and Mcncfce, E., On the effect of dimethyl sulfoxidc on hair kcratin, J. Invest. Dermatol., 49,297-301 (1967). (7) Swccncy, T. M., Dowries, A.M., and Matoltsy, A. G., The effect of dimethylsulfoxide on the epidermal water barrier, Ibid., 46,300 (1966). (8) Crounsc, B. G., The association of lipids with keratinous proteins of human callus. Ibid., 46,550-4 (1966). (9) Elfbaum, S. G., and English, M. ¾., unpublished observation.