166 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 18 i i i i i i i -10 10 30 50 70 90 110 130 Time (min) Figure 4. Apparent water loss after application of water-free glycerol (4 mg/cm 2) to a glass slide. The initial decrease in the apparent water loss at five minutes suggested that water was being adsorbed into the glycerol. By 30 minutes, the apparent water loss had returned ro zero where ir remained for the rest of the study. 3 -1 -2 -3 i i i i i i i -10 10 30 50 70 90 110 130 Time (min) Figure 5. Effect of glycerol on TEWL. An application of 4 mg/cm 2 of water-free glycerol caused an immediate reduction in TEWL. It remained reduced over the entire two-hour study.

EVALUATING BARRIER FUNCTION 167 compound such as glycerol does not interfere. Thus, all cosmetic materials and products applied to the skin for the purpose of investigating their effect on TEWL should be tested on an artificial support, such as a glass slide, to check for interference. This has the advantage of removing the product-skin interaction and allowing one to focus on any interaction between the product and the evaporimeter. The calibration of the evaporimeter should also be checked after making measurements involving products containing volatile organic solvents, as the products may adsorb onto the polymeric surfaces of the probe and affect the calibration. Finally, interpretation of the data in terms of changes in the barrier function of the skin should be done cautiously with regard to the components of the applied product and with respect to the length of time after application that the measurements were taken. ACKNOWLEDGMENTS The author thanks Ms. A. Solbeck and Ms. J. Harding for their valuable assistance during these experiments. REFERENCES (1) G. E. Nilsson, Measurement of water exchange through skin, Med. Bid. Eng. Comput., 15, 209-218 (1977). (2) T. Frodin and M. Skogh, Measurement of transepidermal water loss using an evaporimeter to follow the restitution of the barrier layer of human epidermis after stripping the stratum corneum, Acta Derm. Venereol., 64, 537-540 (1984). (3) T. Agner and J. Setup, Skin reactions to irritants assessed by non-invasive bioengineering methods, Contact Dermatitis, 20, 352-359 (1989). (4) R. A. Tupker, J. Pinnagoda, P. J. Coenraads, and J. P. Nater, The influence of repeated exposure to surfactants on the human skin as determined by transepidermal water loss and visual scoring, Contact Dermatitis, 20, 108-114 (1989). (5) A.M. Kligman, in The Epidermis, W. Montagna, Ed. (Academic Press, New York, London, 1964). (6) R. Marks, Measurement of stratum corneum function, J. Soc. Cosmet. Chem., 31, 11-18 (1980). (7) R. Blanken, M. J. T. van Vilsteren, R. A. Tupker, and P. J. Coenraads, Contact Dermatitis, 20, 93-97 (1989). (8) M.D. Batt and E. Fairhurst, Hydration of the stratum corneum, Int. J. Cosmet. Sci., 8, 253-264 (1986). (9) M. D. Batt, W. B. Davis, E. Fairhurst, W. A. Gerrard, and B. D. Ridge, Changes in the physical properties of the stratum corneum following treatment with glycerol, J. Soc, Cosmet. Chem., 39, 367-381 (1988). (10) P.M. Elias, B. E. Brown, and V. A. Ziboh, The permeability barrier in essential fatty acid defi- ciency: Evidence for a direct role for linoleic acid in epidermal barrier function, J. Invest. Dermatol., 74, 230-233 (1980). (11) C. F. Parish, "Solvents, Industrial," in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., M. Grayson, Exec. Ed. (John Wiley & Sons, New York, 1983), Vol. 21, pp. 377-401. (12) J. Pinnagoda, R. A. Tupker, P. J. Coenraads, and J. P. Nater, Comparability and reproducibility of the results of water loss measurements: A study of 4 evaporimeters, Contact Dermatitis, 20, 241-246 (1989). (13) K. Grice, H.Sattar, M. Sharratt, and H. Baker, Skin temperature and transepidermal water loss, J. Invest. Dermatol., 57, 108-110 (1971). (14) C. G. T. Mathias, D. M. Wilson, and H. I. Maibach, Transepidermal water loss as a function of skin surface temperature, J. Invest. Dermatol., 77, 219-220 (1981). (15) B. M. Morrison, Jr., unpublished results. (16) Personal communication from Mr. Steve Lako, Vaisala, Inc.