SURFACTANT-SKIN INTERACTIONS 319 leaves few residues there, it does leave materials on skin after a wash that are similar to some of the natural components found in the skin barrier lipids, i.e., fatty acids. We have carried out a detailed electron-spin resonance probe study coupled with direct- binding measurement to quantify the nature and location of such deposits, and this will be reported shortly. Such deposits are quite different from protein-bound anionic sur- factants that induce protein unfolding and stratum corneum damage. Thus, it is quite misleading to conclude that any materiMs left on the skin by a cleansing composition contribute to irritation. Depending on their nature and location, some material may be beneficial, for example, in preserving the composition of the barrier lipids. CONCLUSIONS The ANS displacement from corneum proteins is a sensitive method to study cleanser interactions with superficial corneal layers under realistic washing conditions. Our results show that pure anionic surfactants as well as formulated products containing them vary considerably in their corneum protein binding ability. An isethionate-based cleansing bar leaves consistently less residual anionic surfactants bound to corneum proteins than either a pure soap or a glycerin soap-based bar composition. The results correlate well with their known clinical mildness as measured by the flex wash. The lower protein interactions of the isethionate-based synthetic detergent bar is in part due to the significantly lower protein binding of sodium acyl isethionate, the primary active, relative to soaps. A reinterpretation of the experimental results of an earlier published study was proposed to take account of the competitive nature of anionic dyes and anionic surfactants in binding to substrates like skin. REFERENCES (1) G. Imokawa and T. Takeuchi, Surfactants and skin roughness, Cosmet. Toiletr., 91, 32-46 (1976). (2) G. Imokawa and Y. Mishima, Cumulative effects of surfactants on cutaneous horny layers: Adsorption onto human keratin layers in vivo, Contact Dermatitis, 5, 357-366 (1979). (3) M. Kawai and G. Imokawa, The induction of skin tightness by surfactants. J. Soc. Cosmet. Chem., 35, 147-156 (1984). (4) J. C. Blake-Haskins, D. Scala, and L. D. Rhein, Predicting surfactant irritation from the swelling response of a collagen film, J. Soc. Cosmet. Chem., 37, 199-210 (1986). (5) L. D. Rhein and F. A. Sireion, "Surfactant Interactions With Skin," in Surfactant Science Series, M. Bender, Ed. (Marcel Dekker, New York, 1991), Vol. 39, pp. 33-49. (6) M. Rieger, Human epidermal responses to sodium lauryl sulfate exposure, Cosmet. Toiletr., 109, 6 (1994). (7) E. Gotte, Skin compatibility of tensides measured by their capacity for dissolving zein, Proc. of the 4th lnt. Cong. Surface Active Subs. (Brussels), 3, 83-90 (1964). (8) M. S. Wortzman, R. A. Scott, P.S. Wong, N.J. Lowe, and J. Breeding, Soap and detergent bar rinsability, J. Soc. Cosmet. Chem., 37, 89-97 (1986). (9) M. Paye, F. A. Simion, and G. Pierard, Dansyl chloride labelling of stratum corneum: Its rapid extraction from skin can predict skin irritation due to surfactants and cleansing products, Contact Dermatitis, 30, 91-96 (1994). (10) D. D. Strube, S. W. Koontz, R. I. Murahata, and R. F. Theiler, The flex wash test: A test method for evaluating the mildness of personal washing products,J. Soc. Cosmet. Chem., 40, 297-306 (1989). (11) L. Styrer, The interaction of a naphthalene dye with apomyoglobin: A fluorescent probe of non-polar binding sites, J. Mol. Biol., 13, 482-495 (1965).

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