THE EFFECT OF COSMETIC EMULSIONS ON THE STRATUM CORNEUM By DONALD H. Pow•.v.s and CHAV. L•.S Fox* Presented September 18, 1958, International Symposium, Gesellschaft Deutscher Kosmetik Chemiker, Bonn, Germany IN DEVELOPING cosmetic creams and lotions the cosmetic chemist is faced with t•he task of preparing not only a stable product but one that will have good consumer acceptance. Preparing a new emulsion for the application to the skin with acceptable shelf life may be a difficult task especially when one attempts to incorporate the promotional "plusses" that marketing must have but this could very well be child's play compared to the decision as to what characteristics the consumer would like to see in the product and how to evaluate the efficacy of the product. What is still more of a challenge is the fact that many emulsion properties are discussed daily among cosmetic chemists with no means at hand for measuring these characteristics. For example, experts in cosmetic product development will agree that an outstanding product should (1) possess a certain degree of "slip," (2) dry quickly, (3) leave just the merest trace of oiliness, (4) leave a velvety "feel," (5) leave a smooth finish, etc. But all these characteristics are purely subjective--the end result desired, of course, is a soft, smooth skin. In trying to arrive at what properties the consumer looks for, one may resort to panel testings but the authors have found them of little value in arriving at an answer. True, panel tests are effective in detecting serious flaws in the product, such as evidence of irritation, but they are of little help in actually determining the efficacy of the product. Many of you have, undoubtedly, experienced the situation where two creams identical in every respect except for odor are panel tested. Yet, the results obtained would indicate that the products are poles apart as regards "feel, .... finish, .... slip, .... stickiness, .... skin smoothness," or "greasiness." What is more disturbing is the case where the identical product is tested by a panel of cosmetic chemists on the one hand and by a panel of ad- vertising and marketing personnel on the other with opinions as to "feel," * Warner-Lambert Research Institute, Morris Plains, N.J. 109

110 JOLRNAL OF THE SOCIETY OF COSMETIC CHEMISTS "slip," "finish," "smoothness," and efficacy ranging from good to poor and usually in wide disagreement. In this case, is performance or promotion more important for lasting sales ? A more reliable opinion can be obtained by increasing the size of the panel from a few dozen to a few thousand people and still better results can be obtained by clinical evaluation by experts, but these methods are costly and are usually reserved for the product when it is complete. But how can the cosmetic chemist know if his formulations are on the "right track?" It would help tremendously to be able to measure thosd properties that are desirable and assign a value to these parameters in place of the subjective terminology used in the present state of the art. When this happens cosmetics will come a step closer to being a science rather than an art. One of the functions of the majority of creams and lotions prepared for the skin is to soften the stratum comeurn. For many years it was felt that the oils and waxes contained in creams and lotions softened the skin per se(1). However, recent studies by Blank (2) and Peck (3) show that oils and waxes, as such, do not soften callus tissue but that the water content of the callus tissue is the prime factor responsible for its softness and flexibility. Since ancient times oils, fats and waxes of one sort or another have been applied to the stratum corneum to obtain a soft, smooth, supple finish. How is this compatible with the data obtained by Blank (2) and Peck (3) ? The answer now appears to be that a layer of an oily, water-insoluble material applied to the stratum comeurn reduces the moisture loss from the surface of the skin (4). Figure 1 illustrates the mechanism involved. :•:.: :. FILM OF O:.!•L. ........ ': :•x: • •"• •' ', ? -• STRAT U M .,, ,'•.•r • •,.--.,.-,..•,•¾• [•, • •,:•..•:.. ..f.x--'•.•,•: WATER FROM :, .... •- ,' -•. '•,•.' .--•- '-' •," '- ......... -- - '• '•'•-"r' UNDERLYIN(• TISSUE Figure 1.--Schematic representation of the retention of water of diffusion by the stratum corneum of an area of skin covered with a film of occlusive oil (4).