j. Soc. Cosmet. Chem., 37, 387-393 (September/October 1986) Determination of lysosomal acid phosphatase in human skin as a marker of irritation following different surfactant treatments HUGO J. NIGGLI and RUDOLPH ROTHLISBERGER, Cosmira/ SA, Rte. de Chdsa//es 21, CH-1723 Mar/y, Switzerland, Research Company of We//a AG, Darmstadt, FRG. Received June 6, 1986. Synopsis Acid phosphatase activity in tape-strip biopsies of human stratum corneum was determined using p-nitro- phenyl phosphate as substrate following skin treatment of healthy volunteers with different surfactants at various concentrations. As a short-term effect, enhanced reduction of acid phosphatase activity with stronger surfactants and higher surfactant concentrations was detected. When the skin of panellists was exposed to surfactants in the standardized elbow washing test, a significant long-term increase of lysosomal horny layer acid phosphatase was observed after four or eight days following the final surfactant treatment. This long-term response was found to correlate very closely with the visual scoring system of erythema. Therefore, this assay may serve as a valuable tool for the prediction of skin irritancy and mildness of dilute surfactant solutions. Furthermore, this method is inexpensive, convenient, and avoids the use of animal model systems. INTRODUCTION Substantial efforts have been made in recent years to study the influence of surfactants on the skin. Generally, most of the reported assays are based on in vitro test conditions or using animals as model systems and have been reviewed by Lansdown (1) and Protrey (2). A more reliable in vivo technique for prediction and measurement of irritancy on human skin is the soap chamber test which utilizes a visual scoring system (3). Based on a similar scoring system, Frosch introduced the elbow washing test in 1982 (4). How- ever, these methods are subject to interobserver bias as a main problem (5,6). In 1974, Rutherford and Pawlowski (7) identified the utility of determining the release of acid phosphatase from epi'dermal lysosomes or membrane coating granules as a tool for the assessment of skin irritancy. These workers were using a histochemical staining technique and they observed a short-term increase of epidermal lysosomal acid phospha- rase activity after skin treatment with low irritancy compounds. In contrast, Protrey et a/. (8) recently reported enhanced short-term reduction of acid phosphatase activity in human skin treated with stronger surfactants. They inferred that protein denaturation was the most likely cause of their reduced enzyme activity. Theoretically, skin acid phosphatase activity may change in several ways as a consequence of contact with sur- factants. Some substances may directly influence the activity of this enzyme. Addition- 387