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J. Soc. Cosmet. Chem. 26 47-63 (1975) ¸ 1975 Society of Cosmetic Chemists of Great Britain The percutaneous absorption of some anionic surfactants D. HOWES* Presented on 28th August 1974 in London at the IFSCC VIIIth International Congress on 'Cosmetics--Quality and Safety' organized by the Society of Cosmetic Chemists of Great Britain. Synopsis--The irritant action of a SURFACTANT to SKIN may be related to the ability of that surfactant to penetrate the STRATUM CORNEUM and act upon the underlying viable tissues. The PERCUTANEOUS ABSORPTION of some [• 4C] labelled anionic surfactants has been measured in vivo in rats, after both consumer-type applications and applications of longer dura- tion, and the results have been compared with those from in vitro studies using isolated RAT skin and human epidermis. The methodology for both the in vivo and in vitro studies will be outlined and results will be presented from experiments with a series of sodium soaps of normal FATTY ACIDS, sodium LAURYL SULPHATE, sodium LAUROYL ISETHIONATE and sodium DODECYLBEN- ZENE SULPHONATE. The in vivo techniques can also provide information as to the metabolic fate of topically applied surfactants under user type conditions. The usefulness of the in vitro techniques and their shortcomings will be discussed. INTRODUCTION Saponified fats of animal and plant origin are the traditional sur- factants used in toilet soaps and in recent years these have been reinforced by synthetic surfactants of higher surface activity. The function of these surfactants is to solubilize and remove sebum, deposited soil and skin debris, but the fate of topically applied surfactants is not fully documented * Unilever Research Laboratory, Colworth House, Sharnbrook, Bedford. 47