44 JOURNAL OF COSMETIC SCIENCE addition to the contribution of surfactant monomers, to the penetration of the surfactant into the skin. As stressed earlier, depending on the type of surfactant system contacting the skin, electrostatic effects between charged micelies and the charged aqueous pores may need to be considered, in addition to the micelie steric hindrance considerations put forward in this paper, to elucidate the ability of charged micelies to penetrate into the epidermis. In the future, we plan to examine how mixing surfactants affects surfactant penetration into the skin, since results reported in the past using mixed surfactant systems have been utilized as evidence to support the monomer penetration model (5,9-11), which we have shown not to be applicable in the case of SDS. We also plan to investigate the rela- tionship between the penetration of surfactant into the epidermis and the actual damage induced to the barrier properties of the skin. ACKNOWLEDGMENTS We thank Dr. Hua Tang for many useful discussions regarding the preparation of skin samples and other experimental details, as well as on hindered-transport theories. We also thank Dr. Roxanne Pouliot and Allison Fielder for conducting some of the experi- ments and testing the surfactant penetration method. Finally, we thank Dr. Linda Rhein for bringing reference 32 to our attention, as well as for illuminating discussions on surfactant-induced skin irritation. We are grateful to Unilever Home and Personal Care NA for financial support of this work. Peter Moore thanks the Natural Sciences and Engineering Research Council of Canada for the award of a PGS-B scholarship. REFERENCES (1) T. Agner and J. Serup, Sodium lauryl sulphate for irritant patch testing--A dose-response study using bioengineering methods for determination of skin irritation,J. Invest. Dermato/., 95,543-547 (1990). (2) J. A. Faucher and E. D. Goddard, Interaction of keratinous substrates with sodium lauryl sulfate. II. Permeation through stratum corneum, J. Soc Cosmet. Chem., 29, 339-352 (1978). (3) C. H. Lee and H. I. Maibach, Study of cumulative irritant contact dermatitis in man utilizing open application on subclinically irritated skin, Contact Dermatitis, 30, 271-275 (1994). (4) L. D. Rhein, C. R. Robbins, K. Fernee, and R. Cantore, Surfactant structure effects on swelling of isolated human stratum corneum, J. Soc Cosmet. Chem., 37, 125-139 (1986). (5) J. Vilaplana, J. M. Mascaro, C. Trullas, J. Coil, C. Romaguera, C. Zemba, and C. Pelejero, Human irritant response to different qualities and concentrations of cocoamidopropylbetaines: A possible model of paradoxical irritant response, Contact Dermatitis, 26, 289-294 (1992). (6) K.-P. Wilhelm, M. Samblebe, and C.-P. Siegers, Quantitative in vitro assessment of N-alkyl sulphate- induced cytotoxicity in human keratinocytes (HaCaT). Comparison with in vivo human irritation tests, Br. J. Dermato/., 130, 18-23 (1994). (7) K.-P. Wilhelm, A. B. Cua, H. H. Wolff, and H. I. Maibach, Surfactant-induced stratum corneum hydration in vivo: Prediction of the irritation potential in anionic surfactants, J. Invest. Dermatol., 101, 310-315 (1993). (8) K.-P. Wilhelm, G. Freitag, and H. H. Wolff, Surfactant-induced skin irritation and skin repair,J. Am. Acad. Dermato/., 30, 944-949 (1994). (9) T.J. Hall-Manning, G. H. Holland, G. Rennie, P. Revell, J. Hines, M.D. Barratt, and D. A. Bas- ketter, Skin irritation potential of mixed surfactant systems, Fd. Chem. Toxic, 36, 233-238 (1998). (10) L. D. Rhein, F. A. Simion, R. L. Hill, R. H. Cagan, J. Mattai, and H. I. Maibach, Human cutaneous

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