EFFECTS OF COSMETIC INGREDIENTS 261 barrier to the evaporation of water from stratum corneum is not the top of the stratum corneum but lies somewhere between the topmost and innermost cellular layers of the stratum corneum. Glycerol is known not to penetrate stratum corneum appreciably and presumably its application will result in the formation of a layer at or near the top of this epidermal structure. By virtue of its hygroscopicity, glycerol will unquestionably attract water from the low- er layers of the stratum corneum whenever ambient humidity conditions pre- clude absorption from the air. This will result in continuous migration of water molecules through all layers of stratum corneum towards the glycerol layer which, in turn, readily loses water to the atmosphere. The benefits de- rived from the application of glycerol then reside in its ability to move the evaporative layer of skin moisture from somewhere in the center of the strat- um corneum to the very top of the stratum corneum. CONCLUSIONS 1. The stress relaxation modulus and the elastic modulus are sensitive mea- sures of the ability of various cosmetic treatments to affect the viscoelastic behavior of stratum corneum. 2. The water-holding capacity of a system comprising a humectant and stratum corneum is the sum of the component parts. No synergistic effect could be demonstrated. 3. The application of typical cosmetic humectants to the exposed side of the stratum corneum increases the rate of transepidermal water loss. 4. A model to explain the beneficial effects of a moisturizer on the surface of the stratum corneum is proposed. ( Received November 13, 1973) REFERENCES (1) Blank, I. H., Factors which influence the water content of the stratum comeurn, J. Invest. Dermatol., 18, 433-40 (1952). (2) Chudzikowski, R. J., Skin versus the weather, Mir. Chem. Aerosol News, 44, No. d, 35-41 (1973). (3) Rieger, M. M., and Deem, D. E., Skin Moisturizers. I. Methods for measuring water regain, mechanical properties, and transe½idermal moisture loss of stratum corneum, .l. Soc. Cosmet. Chem., 25, 239-52 (1974). (4) Blank, I. H., Further observations on factors which influence the water content of the stratum corneum, J. Invest. Dermatol., 21, 259-71 (1953). (5) Middleton, J. D., and Allen, B. M., The influence of temperature and hmnidity on stratum corneum and its relation to skin chapping, J. Soc. Cosmet. Chem., 24, 239-43 (1973). (6) Hertz, H. G., and Klute, R., The slowing down of proton exchange in aqueous solu- tions of structure breaking ions, Z. Phys. Chem., Neue Folge, 69, 101-7 (1970). (7) Phelps, E. B., and Void, A., Studies on ventilation, I. Skin temperature as related to atmospheric temperature and humidity, Amer. J. Pub. Health, 24, 959-65 (1934). (8) Sheart, C., et al., Investigations on the exchanges of energy between the body and its ,environment, Trans. Amer. Soc. Heat Vent. Eng., 43, 115-20, (1937).

262 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (9) Fox, C., et al., Modification of the water-holding capacity of callus by pretreatment with additives, I. Soc. Cosmet. Chem., 13, 263-79 (1962). (10) Barnett, G., in Balsam, M.S., and Sagarin, E., Cosmetics: Scien•ce and Technolog•l, 2nd Ed., Wiley Interscience, New York, 1972, p. 76. (11) Berube, G. R., et al., Measurement in vivo of transepidermal moisture loss, I. Soc. Cosme•. Chem. 22, 361-8 (1971). (12) Powers, D. H., and Fox, C., A study of the effect of cosmetic ingredients, creams and lotions on the rate of moisture loss from the skin, Proc. Sci. Sect. Toilet Goods Ass., 28, 21-6 (1957). (13) Unpublished results in the files of Warner-Lambert Co., Morris Plains, N.J.