SYNTHESIS OF PC-9 s 259 the formula's cost in manufacturing emulsions on a large scale, it is recommended to have a low content of cholesteraol and a high content of fatty acid in the phase diagram, since the purified cholesterol is a high-cost material. The ratio of PC-9 s: cholesterol: stearic acid, 2:1:7, was used in the multilamellar emulsion formation, which is described in the following experiment. FORMATION OF A MULTILAMELLAR EMULSION The main objective is to use ceramides or pseudoceramides in a cosmetic formulation to improve the barrier function according to the maintenance of the lipid layer in stratum corneum. The improving barrier function of PC-9 s in the skin is mainly due to its ability to form a multilamellar structure with other components in the emulsion. In the phase study of the PC-9S/fatty acid/cholesterol complex system, the ability to form a lameliar structure was determined by the use of the optical microscope. Table I shows an example of a multilamellar emulsion composition using PC-9 s and the stratum corneum lipid. Finally, it was demonstrated that PC-9 s was easily able to form the lameliar structure with emulsifier and oils. A typical configuration of multilamellar mesophase texture, the optical anisotropy of "Maltese crosses" was shown by use of a cross-polarized microscope. It was also dem- onstrated that this aggregation structure in the emulsion was similar to that of human skin lipid lameliar bilayer (Figure 5). SAFETY TEST OF PC-9 s Table II represents the safety test results of PC-9 s, which was carried out with the dispersion state of PC-9 s in olive oil. In tests of acute oral toxicity and acute dermal toxicity with rat and rabbit, the LD5o (median lethal dose) values demonstrated that PC-9 s was very safe. That is, the LD5o of the acute oral toxicity was more than 5 g/kg and the LD5o of the acute dermal toxicity was more than 10 g/kg in rat. The LD5o of the acute oral toxicity was more than 5 g/kg and the LD5o of the acute dermal toxicity Table I Composition of a Pseudo-Stratum Corneum Lipid Emulsion Lipid components Pseudo-stratum corneum lipid emulsion (wt %) Pseudo- PC-9 s 0.6 stratum corneum Cholesterol 0.2 2.3 lipid Stearic acid 1.5 POE (15) glyceryl monostearte 3.0 Emulsifier Glyceryl monostearte 1.5 7.5 Cetanol 3.0 Liquid paraffin 2.0 Oil Olive oil 3.0 5 Thickener Carboxyl vinyl polymer 0.2 0.2 1,3-Butylene glycol 5 Water phase Water 80 85

260 JOURNAL OF COSMETIC SCIENCE Figure 5. Cross-polarized light microscopic photograph of a pseudo-stratum corneum emulsion containing PC-9 s (x400). Table II Safety Test Results of PC-9 s Test Results Acute oral toxicity (rat) Acute dermal toxicity (rat) Acute oral toxicity (rabbit) Acute dermal toxicity (rabbit) Primary skin irritation Eye irritation Skin sensitization Human patch LD5o* 5 g/kg LD5o 10 g/kg LD5o 5 g/kg LD5o 10 g/kg P.I.I.** score = 0 Eye-washing score = 0.67 No eye-washing score = 4.0 Score = 0 Rate = 0% Score = 0 Non-toxic Non-toxic Non-toxic Non-toxic Non-irritating Non-irritating Non-sensitize Non-irritating * LD5o = median lethal dose. ** P.I.I. = primary irritation index. was more than 10 g/kg in rabbit. The primary skin irritation index (P.I.I.) score "0" means that there is not any problem with PC-9 s on the skin. For the eye irritation test, the solid particle of PC-9 s was applied to the eyes directly, and the eye washing group scored 0.67 and the non-washing group scored 4.0. According to the score analysis index, if its score is below 5, it can be classified as a non-irritating material. The human patch test was performed using PC-9 s dispersed in liquid paraffin. The irritation score resulted in "0." These safety test results demonstrate that PC-9 s is a very safe material as a cosmetic ingredient. FAST RESTORATION FUNCTION OF THE MULTILAMELLAR EMULSION ON DAMAGED SKIN (FIGURE 6) If the multilamellar emulsion application assists barrier function, application in vivo on human skin should decrease TEWL. To test this, we compared the barrier effect of the