COLLAGEN SWELLING PREDICTS SURFACTANT IRRITATION 209 branes. This i, vitro technique was used to study the effect of surfactant structure versus activity for a homologous series of alkyl sulfates and alkyl ether sulfates. The maximum in swelling activity was produced by the C12 alkyl sulfate, and this activity was re- duced by ethoxylation. Using this technique, we estimate the irritation potential of various surfactants to be: LAS = SLS = ALS AEOS-3EO AEOS-6E0 AEOS-9EO = Tween 20 The method was used to study the effect of cocamidopropyl betaine on SLS-induced swelling. The betaine decreased the swelling activity of SLS by as much as 45 percent for cetain combinations of SLS and betaine. These results correlate well with those published using a variety of physicochemical techniques. Most importantly, the irritation potentials predicted by this assay agree with those obtained by established i, vivo and i, vitro irritation assays. These results illustrate the utility of the collagen swelling assay as a rapid method to investigate surfactant interac- tions and generate predictive irritation data. The collagen swelling assay can be used to screen ingredients for lack of irritation or anti-irritant qualities and quantify the extent of these effects. The assay is rapid, easy to perform, utilizes a uniform and reproducible substrate available commercially, and can be used on a routine basis as a rapid screening method for anionic ingredients and products. ACKNOWLEDGEMENT We wish to acknowledge Dr. J. Nichols and Helitrex Inc. for their cooperation in optimizing the collagen film for this project. REFERENCES (1) R. F. Witter and W. Mink, Effect of synthetic detergents on the swelling and the ATPase of mito- chondria isolated from rat liver, J. Biophys. Blochem. Cytol., 4, 73 (1958). (2) U. Zeidler and G. Reese, In vitro test for the comparability of surfactants, Proceedings of the Interna- tional Federation of the Cosmetw Chemists Society. Paris, 229-233 (1982). (3) G.J. Putterman, N. F. Wolejsza, M. A. Wolfram, and K. Laden, The effect of detergents on swelling of stratum corneum,J. Soc, Cosmet. Chem., 28, 521-532 (1977). (4) B. R. Choman, Determination of the response of skin to chemical agents by an in vitro procedure. J. Invest. Dermatol., 37, 263-271 (1971). (5) C. R. Robbins and K. Fernee, Some observations on the swelling of human epidermal membrane,J. Soc. Cosmet. Chem., 34, 21-34 (1983). (6) E. A. Tavss, E. Eigen, and A.M. Kligman, Letter to the editor,J. Soc. Cosmet. Chem., 36, 25 1-254 (1985). (7) A.M. Kligman and W. M. Woocling, A method for the measurement and evaluation of irritants on human skin, J. Invest. Dermatol., 49, 78-94 (1967). (8) G. Imokawa, K. Sumura, and M. Katsumi, Study of skin roughness caused by surfactants: A new method in vivo for evaluation of skin roughness, J. Am Oil Chem, Soc., 52, 479-483 (1975). (9) G. Imokawa, K. Sumura, and M. Katsumi, Study of skin roughness caused by surfactants: II. Corre- lation between protein denaturation and skin roughness,J. Am Oil Chem. Sot., 52, 484-489 (1975). (10) L. D. Rhein, C. R. Robbins, and K. Fernee, Surfactant structure effects on stratum corneum swelling, presented at the Annual Meeting of the Society of Cosmetic Chemists, New York (1985). (11) P. J. Frosch and A.M. Kligman, The soap chamber test, J. Am. Acad. Dermatology, 35-41 (July 1979). (12) D. L. Opdyke and C. M. Burnett, Practical problems in the evaluation of the safety of cosmetics, Proceedings of the Scientzfic Section of the Toilet Goods Association, 44, 3-4 (1965).

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