62 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS but is probably due to the fact that penetration occurs from the [14C] soap deposited on the skin. This experiment is the first of a series on the percutaneous absorption of surfactants and shows that although the in vitro systems give some useful data on relative penetrations they do not completely reflect the in vivo situation and extrapolation from in vitro to the user conditions is difficult. The in vivo experiments in this study have not examined the relationships between penetration and the concentration of the applied solution, duration of contact or number of applications. The 15 min applications in this study were an exaggerated 'consumer type' application but a range of contact times from 1 to 20 min with four different concentrations of surfactant are being examined and the effects of multiple application of test solution. It is felt that this type of in vivo study gives data which can be related to human use of all types of products coming into contact with skin. ACKNOWLEDGMENTS I would like to thank Mr C. T. James for the synthesis of the x4C labelled synthetic surfactants used in this study and Mrs A. Cordell for skilful technical assistance. (Received: 1st April 1974) REFERENCES (1) Tregear, R. T. Physical functions of skin, 1 (1966) (Academic Press, London). (2) Wahlberg, J. E. Percutaneous absorption of trivalent and hexavalent chromium (*•Cr through excised human and guinea-pig skin. Dermatologica 141 288 (1970). (3) Maibach, H. I., Feldman, R. J., Milby, T. H. and Serat, W. F. Regional variations in percutaneous penetration in man. Pesticides. Arch. Environ. Health 23 208 (1971). (4) Feldman, R. J. and Maibach, H. I. Regional variations in percutaneous absorption of •4C-cortisol in man. J. Invest. Dermatol. 48 181 (1967). (5) Bartek, M. J., Labudde, J. A. and Maibach, H. I. Skin permeability in vivo: comparison in rat, rabbit, pig and man. J. Invest. Dermatol. 58 114 (1972). (6) Sprott, W. E. Surfactants and percutaneous absorption. Trans. St. Johns Hosp. Dermatol. Soc. 51 56 (1965). (7) Patterson, M. S. and Green, R. C. Measurement of low energy beta emitters in aqueous solution by liquid scintillation counting of emulsions. Anal. Biochem. 1 279 (1960). (8) Bruno, G. A. and Christian, J. E. Determination of carbon-14 in aqueous bicarbonate solutions by liquid scintillation techniques. Anal. Chem. 35 1216 (1961).

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