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).

EFFECT OF COSMETIC EMULSIONS ON STRATUM CORNEUM 111 Water is continuously evapora- ting froIn the surface of the skin (5). This moisture stems from the tiny orifices of the eccrine glands and froIn the underlying tissues. The rate at which this moisture supply reaches the stratum cor- neum is controlled in a large meas- ure by a thin layer of tissue lying just beneath the stratum comeurn called the barrier layer (6). The stratum comeurn has a mesh-like structure made up of a mixture of 60 to 70 per cent of keratin and 30 to 40 per cent of water-soluble com- pounds (7). Normal stratum cor- neum contains 10 to 25 per cent water. Figure 2.--Desiccator fabricated from a glass cylinder, covered with polyethyl- ene snap cap. This water-holding ability of the stratum corneum is probably due primarily to these nonkeratinous, water-soluble, nitrogen-containing coinpounds (7, 8). Thus, a certain amount of the moisture reaching the stratum comeurn is retained by it and accounts for its flexibility and softness. However, it is entirely possible for the stratum comeurn to be deficient in the water binding components (9), in which case a dry scaly skin will result. And, of course, perfectly normal skin will lose moisture and become dry under conditions of low relative humidity (10). Figure 3.--Desiccator assembly showing cylinder, snap caps, gasket, elastic band and bandage clip.