The purpose of this study was to develop instrumental methods for in vivo measurements of skin elasticity and slip for characterizing skin conditions and substantiating cosmetic efficacy. The bio-rheological instruments developed for this purpose were designed to measure responses eguivalent to the sensory perception by the cosmetic users.
For skin elasticity, the instrument measured swelling height of the skin placed under a suction cup with variable pressure. The slip resistance was measured by a reciprocating pick-up probe placed on the skin under a constant pressure.
Using the “Skin Elastomer”, we measured the surfaces of facial parts, finger tips and the innerside of the forearms. The “Skin Age Parameter” which indicates recovering power showed a good correlation with the age. Skin rheograms made before and after the use of a facial mask also showed interesting differences under initial pressure.
Using the “Skin Slip Resistance Meter”, we quantitatively measured slip resistance on different skin surfaces treated with various cosmetics including toning lotion, creams and studied their effects with time.

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Physicochemical properties of β-glycyrrhizin (β-G, a triterpenoid saponin) and α-glycyrrhizin (α-G, a stereoisomer of β-G, newly developed in this study) were examined in connection with cosmetics.
Both α- and β-G's exhibited similarly considerable interfacial activity. However, the aqueous solution of β-G formed extremely rigid gel in acidic media, whereas α-G showed no sign of gelation.
β-G can emulsify various oily materials lying in a wide range of required HLB value, while α-G has the solubilizing ability for several perfume materials.
A series of experiments were carried out to obtain some informations on the solubilizing, emulsifying, and gelling mechanisms of G's by using ¹³C-NMR, scanning electron microscope and various derivatives of G's.
The results suggested that β-G molecule which was found to be cyclically constructed constitutes the micells which in turn orient anisotropically to form the rigid gel and stabilize the emulsion.

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Some water soluble polymers formed “hydrogel” film containing water. This “hydrogel” film was expected to provide natural protective characteristic not found in commonly used low-molecular weight humectants. Film strength and elasticity tests on the polymers gave sodium hyaluronate the highest values under all test conditions.
In vivo tests, surface slip resistance measurement indicated that sodium hyaluronate significantly reduced skin friction resistance and thus increased skin smoothness.
Transepidermal water loss, and skin/polymer affinity measurements revealed that some water soluble polymers formed not a completely occlusive but a water-permeable, a dermal respirable film on skin surface.
In vitro and in vivo test results suggested that ideal water soluble polymers which would be useful as a skin moisturizer should meet the following conditions; (i) Should have a high molecular weight rather than a low molecular weight. (ii) Should have a component of N-compound for better skin affinity. (iii) Should have a distortion-structure to form a tough and flexible film on skin surface. Sodium hyaluronate having a molecular weight in 6×10⁵-9×10⁵ range fulfilled all of these conditions. The optimum combination of these properties is believed to enhance the shin's natural protective mechanism and is chiefly responsible for its outstanding performance as a skin moisturizer. It was confirmed further that lotions containing sodium hyaluronate had pleasant skin feel and was perceptible at a low level of incorporation by the consumers.

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Red No. 204 (Lake Red CBA) has been widely used for make-up products including lipstick. It is an extremely important red pigment, but a contact sensitivity of Lake Red CBA has been reported by Sugai et al. (Contact Dermatitis 3, 249, 1977), and was also confirmed in our laboratory by modified guinea pig maximization test.
By analyzing Lake Red CBA, many organic impurities were detected therein. These impurities were isolated by HPLC and their structural formulae were confirmed by various analytical methods. As a result, many kinds of aromatic azo compounds (subsidiary colors) were found. The subsidiary colors which the structural formulae were confirmed were eleven kinds in which Sudan I (1-phenylazo-2-naphthol) previously reported as a strong sensitizer was included. Then, these confirmed subsidiary colors and the related compounds were synthesized for uses as the standard samples. And the subsidiary colors in Lake Red CBA were quantitatively analyzed and tested for the contact sensitivity. The subsidiary colors were contained in all of eight Lake Red CBA. From the results of the modified guinea pig maximization test of the synthesized subsidiary colors, it was found that each of them was a contact sensitizer, while Lake Red CBA itself was not.
Accordingly, Lake Red CBA free from subsidiary color was investigated. As an analytical result of C acid (2-Amino-5-chloro-p-toluene-sulfonic acid), a raw material for the synthesis, many kinds of aromatic amines which produce the subsidiary colors contained in Lake Red CBA were detected. It was confirmed that Lake Red CBA synthesized with C acid from which aromatic amines were removed as completely as possible contains no subsidiary color. Then, Lake fed CBA was synthesized with the purified C acid to which three types of the typical aromatic amines were added in the fixed quantity. As a result, it was found that the corresponding aromatic azo compounds are produced in proportion to the added amounts of aromatic amines.
Based on the results mentioned above, the manufacturing process of Lake Red CBA free from subsidiary colors was able to be applied for cosmetics.
This concept has been successfully applied to other impartant colors such as Sudan III, Orange II, Quinoline Yellow WS, Quinizarin Green SS, etc. and these purified colors free from contact sensitive impurities have been commercially produced for our use in cosmetic products.

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Automated analysis system was developed to identify and estimate major components of cosmetic products using combination of two analytical methods rapidly and accurately. This system consists of two sub-systems corresponding to the two different groups of analytical data, and a total-system which produces final results by comparing and integrating the output from each sub-system.
In the first ¹³C-NMR sub-system, the chemical shifts of unknown spectrum are compared with the chemical shifts of the sub-structures of cosmetic ingredients, which have been registered in the System/34 as data base, and the sub-structures likely to be present in sample are retrieved. This is followed by the procedure to list up the total-structures (in most cases, expressed as homologous series) of cosmetic ingredients that can be constructed from the retrieved substructures by searching the total-structure data base. All the organic compounds, registered as data base can be retrieved so long as they are present at a level higher than their respective detection limits. At the same time, the approximate contents of individual total-structures retrieved are determined from the ¹³C-NMR signal intensities, and are divided into three ranks, major (rank 3), medium (rank 2) and minor (rank 1).
In the second GC sub-system, the retention time of each peak is compared with those of n-alkanes previously measured under the same conditions, and is converted into MU values which is expressed as the corresponding carbon number of n-alkane. By doing so, each compound shows a definite value regardless of the measuring conditions. Hence, each peak observed in an unknown sample can be identified by comparing its MU values with those of standard compounds registered as data base. At the same time, each ingredient is determined quantitatively from its peak area because of the excellent quantitative performance of GC.
Having such performances as described above, each sub-system can of course be used independently; however, to ensure correct results, it is necessary to compare and integrate the solutions obtained from these sub-systems, The total system is designed to compare the two results qualitatively, extract the components common to the two sub-systems, compare the semi-quantitative values of these common components, and take, as final solutions, only those ingredients which have been confirmed to present in nearly the same amount. Qualitative comparison is performed through comparison of common code #s registered in each data base, while quantitative comparison is executed through signal intensity ranking as described above.

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The effects of lipophilic surfactants with various short ethylene oxide (EO) chain lengths on Cloud Point (CP) and Phase Inversion Temperature (PIT) have peen studied by using homogeneous polyethyleneglycol dodecylethers. The CP of hydrophilic surfactant aqueous solution decreased when lipophilic surfactant was added. The degree of reduction in CP was correlated with Inorganic Organic Balance (IOB) value of the lipophilic surfactant. The PIT of the n-decane-water-nonionic surfactant system also decreased as lipophilic surfactant added. The degree of reduction in PIT was in reverse relation to that of reduction in CP against the IOB value of lipophilic surfactant. These phenomena could be explained by investigating each partition of lipophilic and hydrophilic surfactants contained in the three phases i.e. oil, water and surfactant phases, which appear at PIT.
It was found that the most of nonionic surfactants were distributed to the oil and the surfactant phases. The cantent of lipophilic surfactants in the oil phase decreased and that in the surfactant phase increased, as the EO chain lengths of lipophilic surfactants increased.
It was also found that, when PIT was fixed at 70°C, the average EO chain length of nonionic surfactant existing in the surfactant phase was held almost constant at around 7 under different combinations of nonionic surfactants.

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In order to obtain emulsions highly safe for human skin, a new O/W emulsion system stabilized with insoluble materials was developed. Emulsification methods utilizing Na-montmorillonite (Na-Mont) and various organic polar substances were investigated. Stable O/W emulsions were obtained by combining Na-Mont and particular compounds such as glycerol monopalmitate. The results of DSC and X-ray diffraction measurements showed that Na-Mont formed insoluble complexes with the compounds in this emulsion system. From the results of microelectrophoresis, scanning electron microscopy, and X-ray microanalysis it was found that the complexes surrounded oil droplets and that the droplets were fixed by network structures formed by the interaction of Na-Mont platelets in aqueous phase. These configurations appears to stabilize the emulsions. The authors named this new O/W emulsion system “The Insoluble Complex Emulsion System”. Cosmetic emulsions such as milky lotions, skin creams, cleansing creams and foundation creams can be prepared using this emulsion system. Two of the major advantages of the emulsions are good waterproofing ability and relatively small change in their viscosity or hardness with temperature. Various safety evaluation tests with experimental animals show that the products using this emulsion system are highly safe.

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The structure and formation mechanism of secondary droplets in O/W emulsions and the contribution of their formation to the properties of cosmetic emulsions were investigated.
It was found that the secondary droplets were the aggregates of the emulsion droplets surrounded by liquid crystal of closed lamella type composed of surfactant, fatty alcohol, and water. In order to form secondary droplet emulsion, presence of an appropriate amount of fatty alcohol and optimum HLB range were necessary. The formation mechanism of secondary droplets was attributed to the existence states of fatty alcohol during the emulsification. The physicochemical properties of the emulsion chaged greatly with the formation of secondary droplets; a yeild value was shown in the emulsion and its stability was improved. secondary droplet emulsions possessed water-retaining ability and they showed skin moisturizing effect when they were applied to the skin.
All of these results are generated by the fact that the liquid crystal was formed in the continuous phase of the emulsion, thus fixing the emulsion droplets as well as water.
Cosmetic creams and lotions having excellent stability and skin moisturizing effect can be formulated by the application of those emulsions in which secondary droplets are formed.

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