j. Soc. Cosmet. Chem., 43, 21-36 (January/February 1992) Liquid crystal make-up remover: Conditions of formation and its cleansing mechanisms TOSHIYUKI SUZUKI, MAMI NAKAMURA, HIKARU SUMIDA, and AKIRA SHIGETA, Tokyo Research Laboratories, KAO Corporation, 2-I-3 Bunka, Sumida-ku, Tokyo I3I, Japan. Received June 24, 1991. Presented at the I6th IFSCC Congress, October 9, I990. Synopsis Oily residues of make-up cosmetics tend to remain in the sulcus cutis and pores of the skin. In order to remove them without causing skin irritation, two particular properties are required: 1) immediate disso- lution and/or dispersion of remaining cosmetics with a make-up remover, and 2) the facility of rinsing off the remover containing the residual cosmetics from skin. In order to meet the former need, the remover must be lipophilic, and for the latter, it must be hydrophilic. Therefore, two opposite properties are required in one product. We have been able to overcome this problem by using a lyotropic liquid crystal system. A liquid crystal that consists of a branched alkyl surfactant and a polyol is able to contain a large amount of oil. As it is bicontinuous to both oil and water phases, the oil-based cosmetics can be dissolved and dispersed easily by rubbing skin with the remover. During the rubbing process, a phase transition occurs, thus enhancing the dissolution of the oily impurities due to the disruption of the liquid crystal structure. In the rinsing process, the oil phase that dissolves the oily residues can be removed from the skin by self-emulsification. The sequential cleansing mechanism of rinsing process is 1) reformation, by addition of water, of a lamellar liquid crystal (LC) containing the oily residues, 2) phase transitions: LC -- O/LC -- O/W emulsion, and 3) removal of the emulsion. During these processes, the interfacial tension between oil and water phases becomes very low and forms fine emulsion droplets, which means they can be rinsed off very easily with the dispersion force of Brownian movement. INTRODUCTION Remaining cosmetics, having finished their use at the end of the day, plus accumulated sebum, are considered to be useless dirt. Oily cosmetics such as waterproof foundations, well protected from sweating, eyeshadows, and lipsticks are especially difficult to suf- ficiently cleanse by surfactant types of cleansers and soaps. It is usually considered that solvent-type cleansers such as cleansing creams or cleansing oils are useful for removing 21

22 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the cosmetic residues. However, they tend to remain on the skin because they have not been developed for better removal from the skin after they disperse or dissolve cosmetics. Usually they are wiped off with a tissue however, this method may result in skin damage by the scrubbing motions and in incomplete removal of cosmetics from the skin. Under these circumstances, it is necessary and critical for the cleansers to be rinsable, as well as being able to dissolve and disperse cosmetics efficiently to protect the skin from physical damage. In order to dissolve the oily cosmetics, the cleanser must be lipophilic, which means that it should be an oily type or possess low interfacial tension to the oil (1). On the other hand, in order to be rinsable, it must be hydrophilic. Therefore, to meet both needs, the ideal cleanser must satisfy these two opposite features at the same time. We found that a liquid crystal system consisting of nonionic surfactants and polyhydric alcohols can contain a large amount of oil thus it can cleanse oily dirt well. Moreover, it can be rinsed off very easily by simply washing with water. In this report we discuss conditions of the formation of the liquid crystal, the cleansing mechanism, and the advantages as a make-up remover. EXPERIMENTAL MATERIALS All surfactants used were commercially available. Polyoxyethylene(20) octyldodecyl ether (EOD-20) was used as a nonionic surfactant for the remover. For comparison, variable numbers of ethylene oxides attached to polyoxyethylene octyldodecyl ethers (EOD-n), polyoxyethylene(20)oleyl ether (EO-20), polyoxyethylene(20) sorbitan mono- stearate (ESMS-20), polyoxyethylene(60)sorbitol tetraoleate (ESTO-60), polyoxy- ethylene(15)glycerol monostearate (EGMS- 15), and polyoxyethylene(60)hydrogenated castor oil (EHCO-60) were used (ICao Co.). Tris-(2-ethylhexyl)-glyceride (Kao Co., Excepal TGO) was used as the oil component of the liquid crystal remover. The oil-soluble 2-ethylhexyl-p-methoxycinnamate (Givaudan Co., Parsol MCX), which possesses the maximum absorbance at 290 nm, was used as the marker for the analysis of oily residue. The glycerol used was reagent grade (Wako Chemical Industry Ltd.). Water was deionized and distilled. Materials used for the model oily residue were ceresin (Nikko Rika Co.), microcrystalline wax (Witco Chemical Co.), carnauba wax (Noda Wax), and diisostearyl realate (Nisshin Co. ,), and were of cosmetic grade. D. & C. Red No. 7 and titanium dioxide (Miyoshikasei Co.) of cosmetic grade were used as pigments. METHODS Conditions of skin surface. Conditions of the skin surface were observed and photographed with a direct skin analyzer (DSA) (2), which is a photo-magnifying scope attached to a TV camera and a fiber light unit developed by cooperation of Kao Co. and Scalar Co., with 50 X to 200X magnification of skin images. Morphological study of skin was also made by microscopic obesrvation of skin replicas. Physiological effects of cleansing methods. Two kinds of cleansing methods were carried out once a day throughout the three-week testing period. One was rinsing off with water