286 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Clar (4) has recently published results on skin impedance measurement that, in spite of the variation in the moisture of the atmosphere, when the w/o cream is applied, the moisture of the skin is preserved for some time. However, oil-in-water (o/w) type emulsions have better consumer acceptance than the w/o type emulsion, despite the various benefits of the latter to the skin. This can be at- tributed to the difficulties of maintaining the stability of the w/o emulsion as well as the inferior feel during application. Generally, w/o emulsions are prepared by increasing the ratio as well as the viscosity of the outer phase (oil) in order to improve stability. This results in a product with a transparent and glaring appearance and with a greasy and oily feeling, which will not readily gain consumers' acceptance. It is of great interest for cosmetic scientists to try to eliminate such defects from w/o emulsion (for example, the excessive addition of water caused separation (60 to 70 per cent)). The addition of oil-soluble polyvalent metallic soaps increased the stability of the w/o emulsions to some extent, but hardly altered the application defects. From the above facts, the authors carried out a series of experiments to obtain w/o emulsions, which were designed to hold wide ranges of water ratio, a nongreasy feel, and still have good stability. As a result, it was possible to develop a new emulsification method, which the authors termed as the "gel-emulsification method." The main points of this method are described as follows: By mixing an aqueous solu- tion of amino acids or their salts with lipophilic surfactants having specific require- ments in their chemical structure, a kind of gel, consisting of the surfactant in the continuous phase and an aqueous solution of amino acids or their salts in the dispersed phase, could be formed. In the following emulsification step, the gel was dispersed into the oil phase, and then the water phase was added into the mixture and emulsified. It was possible to obtain a stable w/o emulsion and/or cream having excellent characteris- tics with a wide range of water content. The major characteristics of the creams obtained by this method were their excellent affinity and nongreasy feel to the skin which has never been achieved before with a w/o emulsion. Moreover, the surfactants such as the monoglycerides used in the creams prepared by this gel-emulsification method are highly safe materials found widely in nature and lipids. Furthermore, the amino acids used in this investigation are also found to be in the natural moisturizing factor (NMF) of the skin and safe enough to be used as food fortifiers for human nutritional purposes. From this viewpoint, the creams obtained by the new method have great advantages over existing formulations, since they have been prepared from ingredients which have been proven to be physiologically safe for human beings to use. The research findings will be discussed in 3 parts. First, it will be necessary to clarify the necessary requirements in the relationship between surfactants and amino acids in order to form the gels (which is characteristic in the new technology). Secondly, the details of the gel emulsification method, in which the gel is dispersed into the oil phase and water is added, will be discussed together with its characteristics. Finally, the exam- ples of the practical application of the new technology to actual cosmetic formulations and their characteristics will also be explained. In addition, the similarity existing between the phenomena obtained in connection with amino acids and surfactants, and the spontaneous emulsifying phenomena on the skin will also be discussed to some extent.

WATER-IN-OIL EMULSIONS 287 EXPERIMENTAL GEL FORMATION OBTAINED BETWEEN SURFACTANTS AND AMINO ACIDS Materials: Most of the surfactants used in this study were commercially available. For example, Sunsoft © O-30B* (glycerol monooleate) was used as a standard surfactant for many of the experiments. Whenever necessary, those synthesized in the usual way or those fractionated by molecular distillation were used. The amino acids and their salts were of special reagent grade. Other reagents used were also of the same grade. Distilled water was used throughout the study. METHOD a. Gel Formation.' Surfactants and amino acids or their salts, which were possible to form the gels, were classified by the following simple method. The surfactant was added to an aqueous solution of the amino acid or its salt at room temperature and stirred with a laboratory mixer. A gel was formed as shown in Fig. 1. All of the gels obtained by this method were observed as to their electrical conductivity and their stability in hot water. Figure 2 illustrates this property and only those without electrical conductivity and insoluble in water were selected for further study. b. Other Measurements.' In order to investigate the various functions of the gels, the chemical structure of the surfactants, the structure and properties of the gels obtained, and the effects of amino acids, etc., were examined by the following methods: Figure 1. Example of gels prepared between surfactants and aqueous solution ofamino acids *Taiyo Kagaku Co., Ltd., 62 Akahori, Yokkaichi, Mie, Japan.