312 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VII :. :: Example of w/o Type Emollient Cream Squalane 25.0 parts Ceresine 3.0 Beeswax I, 5 Lanolin 0.5 Petrolatum 6.0 w/o gel 20.0 Propylene glycol 5.0 Water 3 9.0 Perfume proper amount Antiseptics proper amount cosity and uniform particles may be obtained. On the other hand, when unstable gelS:i i are used (or under conditions inducive to gel destruction), unstable w/o emulsions and creams result. In other words, there is a correlation existing between the properties of?i the gel used and the stability of the final emulsion obtained. ß APPLICATION TO COSMETICS As mentioned above, the authors elucidated the requirements for surfactants that.i?: formed stable gel and the function of the amino acid contributing to.the stability emulsions. It was noted therein that the characteristics of the gel used played an portant role, and that the better the gel used in the formulation, the better the sions or creams produced were. We will discuss some of the advantages obtained the application of this emulsification technique in the preparation of cosmetic together with the characteristics of the finished products. Several creams were pared by the gel-emulsification method and used as a base for cosmetics. From the measured values and stability of the prepared creams by this method, noted many advantages with this emulsifying method and products. For example, any type of cream with required values may be readily selected by referring to the'•)?• component ratio, and a stable cream may be obtained by adding a definite quantity the gel to cover the wide ranges of volume ratio. Even those at the range of extremelY/i:'•} biased volume ratio where another surfactant such as soaps are used to adjust HLB stabilizing the system can also be used. Furthermore, from the evaluation of the application tests, we were able to know th e suitable formulation ranges for 3 types of creams such as the cleansing, massage, and'-j!:ii emollient types, respectively. It was especially interesting to note that suitable formula'i:':!? tions for emollient creams were concentrated in the ranges, wherein there was a large content of water contrary to the former 2 creams. By using these new techniques and know-how in the formulation of cosmetics, the authors were able to prepareT!i: various types of bases for cosmetics. An example of the emollien.t cream is shown in'? Table VII. This method may be applied not only to cosmetic creams, but also to stick type emulsion products with extremely low water content and also to different pharma-' :' ceutical preparations. The characteristics of the cosmetic bases prepared by using this ß' method were their ready adaptation to the skin, their excellent spreadability and j3 moisturizing effect with hardly any greasy feel and glaring appearance, which were ..

WATER-IN-OIL EMULSIONS 313 common to conventional w/o type cosmetics. In addition, the products were highly safe for skin application. These many advantageous characteristics of the creams may be at- tributed to the phenomena suggesting the role of NMF. The stability of these products were excellent and had long shelf life, even at elevated temperature together with less dependability of hardness on aging and temperature. It is well known that the NMF content in stratum comeurn is high and has water absorbing and water holding properties. It is said that the chapping of the epidermis in the winter and the dryness of the aged skin are due to insufficient secretion of sebum and NMF. In view of this fact, it is quite natural and reasonable to supply the deficiency of NMF with cosmetics. NMF is said to be found mostly at the boundary below the stratum comeurn and is found also in stratum granulosum and sweat. Sixteen free amino acids have been identified such as serine with more than 30 per cent, glutamic acid, proline, etc. (7). It has been proven that mono-, di- and triglycerides of fatty acids also exist in sebum. Sebum flows readily and spreads on the surface of skin after reach- ing the hair follicles and is then mixed with sweat and eventually forms a skin surface lipid film which is a w/o type emulsion. It is easily inverted to o/w type emulsion under the condition when the ratio of sweat becomes high. But, this is reversible and the type emulsion is determined depending upon the physiological condition of the skin surface (w/o, --• o/w) (8). We can find an interesting similarity between the natural emulsification phenomena on the skin surface and that of the gel-emulsification method developed by the authors. As mentioned before, in our emulsification method, monoglyceride, and aqueous solution of amino acid which correspond to sebum and NMF, respectively, were mixed and a w/o type emulsion was formed. On the contrary, urea and uric acid, which are found in sweat broke down such w/o emulsions and inverted to that of the o/w type. Further- more, when the gel was kept in water, it expanded remarkably. This property is similar to semipermeability of the lipid film. As the amino acids in the gels retard moisture loss and maintain moisture by their strong hydration effect, it is considered that cosmetic bases utilizing amino acids play an important role in maintaining the flexibility and elas- ticity of the skin. The effect of products formulated with amino acids on the skin are now under investigation by the authors from the view point of viscoelasticity of stra- tum comeurn and percutaneous absorption of amino acids using radioisotope. CONCLUSION The w/o emulsions stabilized with amino acids or their salts were investigated. The following may be concluded. 1. Stable w/o type emulsions which have the capacity to contain wide ranges of water ratio, were obtained by using the gels prepared in a given combination of the amino acids and their salts with lipophilic surfactants having high orderly lameIlar structures. 2. The authors applied this technology to the formulation of cosmetics such as creams, stick type cosmetics, foundations, etc. 3. The outstanding characteristics of the products obtained by using this method are their refreshing, smoothing, ready adaptation to the skin and moisturizing effects