OCCLUSIVITY OF OIL FILMS 355 Table IV Relationship of Casual Lipid Level with TEWL(C), Skin Surface Temperature, and Occlusivity of Solid Paraffin in Emulsion Form Range of Casual Number Average Average Skin Lipid Level of TEWL(C) Temperature (mg/cm •) Persons (mg/cm2/h) (øC) Average Occlusivity of Solid Paraffin Emulsion After 120 minutes (%) 30-40 2 0.92 33.7 32 40-50 6 0.59 32.8 57 50-60 5 0.36 31.4 72 60-70 2 0.53 32.7 59 prevent the skin from drying (13). Therefore, it is possible that the occlusive effect of oil films in those subjects having a high lipid level may be rather higher than in the subjects having a low lipid level even if the application method is the same. In order to verify this, the experimental results obtained in the above experiments were examined in relation with the surface lipid level. The results are summarized in Table IV. Although the number of the subjects examined were not large enough for statistical analysis, it was observed a tendency of smaller value of TEWL(C) and higher occlusive effect of oil films in the subjects with a higher lipid level. This implied that the occlusive effect of emollients was smaller on dry skin than oily skin by the same application method, which presented an interesting aspect from a standpoint of skin care. CONCLUSION It has been known that the occlusive effect of oils depends on the type of oils and their coating amount. However, it was further found in the present work that the occlusive effect also depended on other factors such as physical form of the oils, emulsion type, and droplet diameter of the emulsions. It was found that differences in the adhering states of the oil films on the skin were responsible for the observed changes in the occlusive effect. Although emulsions are generally used for cosmetic creams because of their sensory advantages, it was also found that they played an important role from a standpoint of skin care. Namely, solid paraffin showed a remarkable occlusive effect when applied uniformly on the skin surface, but it showed no occlusive effect when applied nonuniformly. In order to apply solid paraffin uniformly, the use of its emulsion was found to be the most suitable technique. In other words, it is possible to obtain a liquid state of solid paraffin at room temperature when emulsified, thus solid paraffin can be applied uniformly on the skin surface, forming a flexible and occlusive film. It was shown that the occlusive effect was low for persons having a low lipid level. This implied that the use of a cream with a high occlusive effect is important for dry skin. Therefore, for dry skin, it is suitable to apply those creams having fine emulsion droplets of solid oils since the occlusive effect of solid oils increases with the decrease in their emulsion droplets.

356 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS REFERENCES (1) I. H. Blank, Factors which influence the water content of the stratum corneum, J. Invest. DermatoL, 18, 433-440 (1952). (2) B. Idson, Dry skin, moisturizing and emolliency, Drug Cosmet. Ind., 117, (4) 43-45, 141 (1975). (3) D. H. Spruit, Interference of some substances with water vapor loss of human skin, Amer. Perfum. CosreeL, 86, (8) 27-32 (1971). (4) D. H. Powers and C. Fox, A study of the effect of cosmetic ingredients, creams and lotions on the rate of moisture loss from the skin, Proc. Sci. Sec. T. G. A., 28, 21-26 (1957). (5) K. Okamoto and T. Kondo, Effect of ointment base on insensible perspiration, Yakuzaigaku, 29, (3) 207-212 (1967). (6) D. H. Powers and C. Fox, The effect of cosmetic emulsions on the stratum corneum,J. Soc. Cosmet. Chem., 10, 109-116 (1959). (7) H. Baker, Experimental studies on the influence of vehicles on percutaneous absorption, J. Soc. Cosmet. Chem., 20, 239-252 (1969). (8) O. Jacobi, Nature of cosmetic films on the skin,J. Soc. Cosmet. Chem., 18, 149-160 (1967). (9) R. S. Greene, D. T. Downing, P. E. Pochi and J. S. Strauss, Anatomical variation in the amount and composition of human skin surface lipid,J. Invest. Dermatol., 54, 240-247 (1970). (10) H. Baker and A.M. Kligman, Measurement of transepidermal water loss by electrical hygrometry, Arch. Derm., 96, 441-452 (1967). (11) K. Grice, H. Satter, M. Sharrat and H. Baker, Skin temperature and transepidermal water 1oss, J. Invest. Dermatol., 57,108-110 (1971). (12) Y. Kita, S. Matsumoto and K. Yonezawa, Permiation of water through the oil layer in w/o/w type multiple-phase emulsions,J. Chem. Soc. Jap., 1978 (1) 11. (13) v. R. Wheatley, The nature, origin and possible functions of the cutaneous lipids, Proc. Sci. Sect. T. G. A., 39, 25-28 (1963).