METHOD FOR TRANSEPIDERMAL WATER LOSS 117 ß Untreated •- t v Castor Oil E-= 500 ..... .a 4oo- •._. 300 •- o 200 o._j 100 - o 1 2 3 4 5 6 7 24 Time (hours) Figure 6. TEWL rates vs time values for untreated skin and skin treated with castor oil. Bars refer to standard error of measurement. with adsorption of water onto a desiccant. The new method proved to be very efficient. TEWL equilibrium could be achieved within three hours and a full study can be com- pleted within eight hours. Cartilage-stripped hamster ear skin was successfully used as an in vitro membrane for TEWL measurement. The barrier properties of the hamster ear skin compared favorably to those of human skin. TEWL rate values agreed with values previously reported for human skin obtained under similar environmental conditions (1,2). The membrane exhibited an exponential increase in TEWL with increased temperature. A calculated energy of activation for water permeation of 13 Kcal/mole was in general agreement with the value reported previously by Scheuplein for human skin (9). Table II Transepidermal Water Loss Values for Mineral Oil Conditioning Ear After Various Time Periods Time Periods: 1 hr 3 hr 6 hr 24 hr Treated Ear Mean TEWL I-tg/cm2/hr Mean TEWL }zg/cm2/hr 391 269 268 2O6 Untreated Ear 437 315 226 2O2 p 0.3 p 0.3 p 0.3 p 0.3

118 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The present in vitro technique potentially can also be used to evaluate the relative effec- tiveness of skin agents. This method has a real advantage in that the tritium-tracer technique can eliminate erroneous TEWL values that may result from water evaporation from a moisturizer. In general, it would appear that TEWL is influenced by the polarity of the agent applied to the skin. The most nonpolar of the four agents tested, namely mineral oil, showed the lowest TEWL rate. In contrast, the humectant, (25% glycerin in water)-treated skin, showed an increase in TEWL rate. Our TEWL rates for glycerin were comparable to data previously reported by Reiger and Deem (30). Occlusive agents, such as mineral oil, showed evidence of decreasing water loss by acting as a physical barrier to the transport of water through the membrane. Further work is deemed necessary for proving the validity of this method as a pretest for moisturizer efficacy. REFERENCES (1) I. H. Blank, Factors which influence the water content of the stratum corneum, J. Invest. Dermatol., 18, 433-439 (1952). (2) I. H. Blank, Further observations on factors which influence the water content of the stratum cor- neum, J. Invest. Dermatol., 21, 259-269 (1953). (3) N. Brudney, M. Leduc, and B. Turek, Effects of vehicles on percutaneous absorption, Cosmet. Toilet., 93, 53-66 (1978). (4) H. D. Onken and C. A. Moyer, The water barrier in human epidermis, Arch. Dermatol., 87, 584-590 (1963). (5) R. J. Scheuplein and I. H. Blank, Permeability of the skin, Physiol. Rev., 51(4), 702-747 (1971). (6) H. Baker and A.M. Kligman, Measurement of transepidermal water loss by electrical hygrometry, Arch. Dermatol., 96, 441-452 (1967). (7) G. E. Burch and T. Winsor, Rate of insensible perspiration (diffusion of water) locally through living and through dead human skin, Arch. Intern. Med., 74, 437-444 (1944). (8) J. W. H. Mali, The transport of water through the human epidermis, J. Invest. Dermatol., 27, 451-469 (1956). (9) R. J. Scheuplein, Mechanisms of percutaneous absorption. I. Routes of penetration and the influence of solubility, J. Invest. Dermatol., 45(5) 334-346 (1965). (10) R.J. Scheuplein and R. Bronaugh, Biochemistry and Physiology of the Skin (Oxford University Press, 1983), pp. 1255-1295. (11) S. Nacht, Skin friction coeffient: Changes induced by skin hydration and emollient application and correlation with perceived skin feel, J. Soc. Cosmet. Chem., 32, 55-65 (1981). (12) J. D. Middleton, The mechanism of water binding in stratum corneum, Brit. J. Dermatol, 80, 437-450 (1968). (13) J. D. Middleton and B. Allen, The influence of temperature and humidity on stratum corneum and its relation to skin chapping, J. Soc. Cosmet. Chem., 24, 239-243 (1973). (14) M. S. Christensen, Viscoelastic properties of intact human skin: Hydration effects, and the contribu- tion of the stratum corneum, J. Invest. Dermatol., 69(3), 282-286 (1977). (15) B. Idson, Cosmetic dry skin, moisturizer, emollients, and emulsions, Cosmetic Technology, 32-34 (1982). (16) A. Kligman, Regression method for assessing the efficacy of moisturizing, Cosmet. and Toil., 93, 27-35 (1978). (17) J. L. Leveque, Biophysical characterization of dry facial skin, J. Soc. Cosmet. Chem., 82, 171-177 (1987). (18) P. Flesch, Chemical basis of emollient functions in horny layers, Proc. Sci. Sect. Toilet Goods Assoc., 40, 1-7 (1963). (19) M. S. Wu, Determination of concentration-dependent water diffusivity in a keratinous membrane, J. Pharm. Sci., 72(12), 1421-1423 (1983).