j. $oc. Cosmet. Chem., 30, 345-356 (November 1979) Study on the occlusivity of oil films HISAO TSUTSUMI, TOSHIAKI UTSUGI and SHIZUO HAYASHI Kao Soap Co., Ltd., Tokyo Research Laboratories, 2-1-3 Bunka, Sumida-ku, Tokyo 131, Japan. Received January 18, 1979. Presented IOth I.F.S.C.C. Congress, October 1978, Sydney, Australia. Synopsis The OCCLUSIVITY of oils was determined in vivo by measuring the suppression of transepidermal water loss (TEWL) of the skin. Various emollients were applied to human skin in various forms, including powder, solution and emulsion of different types having different size distributions, and the residual states of the OIL FILMS on the skin surface were examined with time. In order to discuss the occlusivity in relation to the individual skin conditions, the surface temperature of the skin and casual lipid level were also determined in each subject. The following are the results obtained from these experiments: 1) the occlusivity of the oil films varied with time, type of oils, their coating amount, physical forms, emulsion type and droplet diameter of the emulsion and 2) the occlusive effect of oils also depended upon the characteristics of the skin such as casual lipid level and TEWL. These results could be explained by the differences in uniformity, spreadability and porosity of the oil films on the skin surface in the residual state. It is believed that the emolliency of the oil can be influenced by these differences. INTRODUCTION It has been always the aim of cosmetic chemists to maintain the skin's softness and freshness and it is considered important to retain moisture in the stratum corneum (1). Emollients, serving not only as lubricants but also forming occlusive films on the skin which retard the water loss from the stratum corneum, render the skin supple and flexible. In this respect, therefore, the emollients have been often termed "occlusive moisturizers" (2). A large number of works have been reported on the theory and measurement of the resistance to water vapor loss of the layer of emollients (3-7). Although their experimental conditions and interpretation of the results differ, it is generally observed that hydrocarbons such as petrolatum strongly inhibit water loss whereas synthetic esters with branched chain tend to transmit water through because of their porosity (8). Unfortunately, there have not been many previous published reports on the effect of the differences in the states of occlusive films on emolliency. Since the occlusivity of the oil is believed to depend greatly on its state on the skin surface, the present study was undertaken to investigate the relation between the residual state of the oil on the skin surface and its occlusive effect. In order to vary the adhering state of oil films, oils 345

346 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS were applied to the skin directly in their neat form and also in the form of their chloroform solution or emulsion. Various emulsions were examined by changing the types of emulsion and particle size distributions. The occlusivity was then examined with these different types of oil samples. The present paper discusses the desirable state of oil films and suitable physical forms of oils for the application from the standpoint of skin care. EXPERIMENTAL MATERIALS Solid paraffin with a melting point of 48øC, petrolatum, and liquid paraffin obtained from Wako Pure Chemical Industries, Ltd., were used as oil ingredients they were of pure grade. Various forms of samples including neat, solution, and emulsion of these oils were prepared. Liquid paraffin with or without 5% of polyoxyethylene stearyl ether was used as neat samples. Solid paraffin with or without 5% of polyoxyethylene stearyl ether was ground into a powder form and employed as neat samples of solid paraffin. The solutions of these oils were prepared by dissolving them in chloroform of extra-pure grade. Oil-in-water emulsions of liquid paraffin and solid paraffin were prepared and stabilized with 5% of polyoxyethylene stearyl ether. O/W type emulsions of these oils having a different particle size distribution were also prepared using a different ratio of emulsifier mixtures of polyoxytehylene (20) sorbitan monooleate and sorbitan monooleate. Using 5% of sorbitan sesqui-oleate, a w/o type emulsion of liquid paraffin was prepared and used. All of the emulsifiers used were commercial materials of Kao Atlas Co. A Coulter Counter (Model TA-II, Coulter Electronics Inc.) was used to determine the particle size distribution of o/w type emulsions and their mean droplet diameter was calculated. The subjects used for this experiment were 32 healthy human males and females ranging in age between 18 and 31. PROCEDURE Measurement of TE Samples containing 4.5 to 5.4 mg of oil ingredient to be examined were applied with a microsyringe to a 1.5 cm x 1.5 cm area of the inner surface of the forearm in each subject. Each sample was spread to form its film with the microsyringe in a certain manner without rubbing. TEWL of the treated skin of the individual subiects was measured intermittently for 2 hr after the application of the samples using an electronic hygrometer, Evaporimeter EP-I (Servo Med in Sweden) equipped with a sensor having a diameter of 10 ram, at 21 to 23øC and 35 to 48%RH. TEWL of untreated skin adiacent to the treated skin was also measured as control at the same time. In order to discuss the occlusivity in relation with the individual skin conditions, the skin surface temperature and casual lipid level were also determined on the forearm in each subject using a usual method (9). Observation of Oil Film The residual state of oils on the skin surface was observed with time using a stereomicroscope (Wild, M-8) after the application of the samples. An additional