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j. Soc. Cosmet. Chem., 29, 717-725 (November 1978) Characterizing aluminum-skin interaction by an electrometric technique DAVID T. FLOYD Cyanimid Consumer Research Center, 697 Route 46, Clifton, NJ 07015. Present address NL Industries, Inc., P.O. Box 700, Hightstown, NJ 08520. Received December 2, 1977. Presented at Annual Scientific Meeting, Society of Cosmetic Chemists, December 1977, New York, New York. Synopsis Observed differences in the antiperspirant behavior of ALUMINUM chlorohydroxide and aluminum chloride have been attributed to differences in their INTERACTION WITH SKIN. The literature contains many references to methods for measuring the interactions of exogenous materials with skin. The electrical properties of skin have been used successfully as a means by which to describe this effect and it was thought appropriate to investigate this approach with respect to aluminum salts. Instrumentation and techniques for measuring the electrical impedance of excised epidermal membrane were developed. The effecis of two aluminum salt antiperspirants on the impedance of guinea pig stratum corneum were measured. Aluminum chlorohydroxide reduced the impedance five times more than aluminum chloride. The results are in agreement with reported skin sorption behavior for these salts and with their antiperspirant activities in vivo. The hypothesis that antiperspirancy is based in part on antiperspirant/skin interaction is supported by the present study. The ELECTROMETRIC method described herein was found to be a viable TECHNIQUE for studying these interactions. INTRODUCTION The antiperspirant profiles of aluminum chloride and aluminum chlorohydroxide have been studied extensively in recent years (1,2). These studies indicated that at low concentration ( 0.44M AI), aluminum chlorohydroxide exhibited greater antiperspirant activity, but as the concentration and/or the contact time was increased, the effect of the aluminum chloride became more intensified and surpassed that of aluminum chlorohy- droxide. These differences in the bioavailability patterns of the two salts were suggestive of differences in their interactions with stratum comeurn. Dermatological literature describes the stratum comeurn as a barrier which is quite resistant to penetration by exogenous agents (3-10). It has been demonstrated that this barrier function can be related to the electrical impedance properties of the skin (6,11-17). A comprehensive review and discussion of the factors governing the passage of electricity across the skin have been written by Tregear (6), and evaluated by others (11, 13, 14, 18). 717