THE INTERACTION OF DETERGENTS AND THE HUMAN SKIN 19 1. Different classes of detergents damage the skin in different ways. 2. The final effect of a detergent on the skin is the product of penetration and toxicity. In our in vitro tests we measured only one parameter at a time. 3. The differences for the soap (T6) between the results of the patch tests (strong irritation) and the immersion tests (no irritation) might be explained in the following way: Blank and Gould (16) found that the sodium laurate soap irritates at pH 7.5, but not at pH 9.5. They state that at pH 7.5 free fatty acids are split off that penetrate more easily through the stratum corneum than soaps, because of their favourable water/ether partition coefficient. These readily-penetrating fatty acids are irritating to the living skin. This has also been shown during investigations on acne vulgaris. Smeenk was able to establish that in patch testing, a soap solution is neutralized, which may result in the splitting-off of fatty acids. In the im- mersion test on the other hand, the pH of the soap solution remains alka- line, with the result that no fatty acids are formed. 4. The in vitro tests are carried out under circumstances differing so greatly from what actually happens when living skin is exposed to deter- gents, that comparison is impossible. CONCLUSIONS Two questions posed at the beginning of my talk can now be answered. Detergents can irritate a normal skin. Obviously, Suskind's results are only valid for the detergents which he used and for his experimental conditions their application to all detergents under all conditions is not warranted. Furthermore, he studied the hands primarily. In our experiments the skin of the arms proved to be mure sensitive. The question of whether detergents may cause a chapped skin was also answered in the affirmative. It has been proved that under the same atmos- pheric conditions some detergents may cause a chapped skin, while others do not cause this condition. Summarizing our other results we can state that various tests considered for the evaluation of a detergent do not give results that concur with those obtained with the immersion test, which is the best simulation of-actual use. Finally, I have had an opportunity to tell you about effects we observed with respect to the washing out of water- soluble substances by various detergents from the skin, and the implications of this for the condition of the stratum corneum. I am not yet able to develop a comprehensive theory covering everything that happens in human skin exposed to washing procedure. Our next step in the study of

2O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS our problems will be to compare the toxicity of various detergents for the living epidermal cell. As the technical difficulties are considerable, this will keep us busy for the next few years. (Received.' 1st September 1967.) REFERENCES (1) Van der Meiren, L. and Achten, G. Huid en Allergie, dl. IV (1961) (Stenfert KroeseN.V., Leiden). (2) Jacobi, O. Berufsdermatosen 6 35 (1958). (3) Bettley, F. R. Brit. Med. J. 1 1675 (1960). (4) Cooke, M. A. Trans. St. John's Hosp. Dermatol. Soc. 51 7 (1965). (5) Gaul, L. E. and Underwood, G. B. J. Invest. Dermatol. 19 9 (1952). (6) Blank, J. H. J. Invest. Dermatol. 18 433 (1952). (7) Carter, R. O. and Griffith, J. F. Toxicol. Appl. Pharmacol. ? 60 (1965). (8) Suskind, R. P. et al. Arch. Dermatol. 88 117 (1963). (9) Jambor, J. J. J. Invest. Der•natol. 9.4 387 (1955). (10) Kligman, A. B. The Epidermis, Eds. Montagna, W. and Lobitz, W. C. (1964) (Academic Press, New York and London). (11) Szakall, A. Arch. Klin. Exptl. Dermatol. 9.01 331 (1955). (12) Spier, H. W. and Pascher, G. Aktuelle Probleme der Der•natologie I (1959) (Karger, Basel and New York). (13) van Scott, E. J. and Lyon, J. B. J. Invest. Dermatol. 9.1 199 (1953). (14) Draize, J. H. Appraisal qf the safety of chemicals in foods, drugs and cosmetics. 2nd edn. 46 (1965) (Association ooe Food and Drug Officials, U.S.A.) (15) Smeenk, G. and Polano, M. K. Trans. St. John's Hosp. Dermatol. Soc. 51 90 (1965). (16) Blank, J. H. and Gould, J. J. Invest. Der•natol. 87 485 (1961). (17) Vermeer, D. J. H., et al. Dermatologica 189. 305 (1966).