342 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS This second mechanism should be the prevailing one in dry skin and should confirm the role of intercellular cements in the maintenance of the barrier function of the S.C. The other explanation of the TEWL increase in the case of "dry skin" is the lack of lipids in the membrane corneum cells. These lipids in bilayer arrangement should be the cause of the high resistance of S.C. to water vapor diffusion. The role of lipids in hydration maintenance has been previously described (19). The main difficulty in studying the relationship between TEWL and temperature is the occuring of sweat with temperature. But such a study should allow the determination of the relative importance of these two mechanisms. The measurement of the lipid content of S.C. should also be of great interest in the knowledge of this problem. In vivo, numerous physical experiments have been proposed to study the difficult clinical problem of dry skin, but most methods modify the properties of S.C. by interacting with it furthermore, underlying tissues often mask the effect which is due to S.C. alone. On the contrary, because it is entirely determined in the few microns of S.C., TEWL measurement constitutes the very sensitive and accurate index of S.C. properties and functional state. REFERENCES (1) I. H. Blank, Further observations on factors which influence the water content of the stratum comeurn,.]. Invest. Derm., 21,259, 1963. (2) A. B. Goodman and A. V. Wolf, Insensible water loss from human skin as a function of ambient vapor concentration,.]. ,qppl. Physiol., 26, 203-207, 1969. (3) D. Spruit and K. E. Malten, The influence of the humidity of the air on the measurement of the water permeability of the skin, Annali Ital. Derre. Clin. sper. 23, 93-115, 1969. (4) K. A. Grice, H. Sattar and H. Baker, The effect of ambient humidity of transepidermal water loss,.]. Invest. Derm., 58, 343-346, 1972. (5) C. Johnson and S. Shuster, The measurement of transepidermal water loss, Br. J. Derre., 81, 40-46, 1969. (6) D. Spruit, The water barrier and its repair. Epidermal wound healing conf., 137-158, 1971. (7) H. Baker and A. Kligmann, Measurement of transepidermal water loss by electrical hygrometry, ,qrch. Derre., 96, 441-452, 1967. (8) L. O. Lamke and B. Wedin, Water evaporation from normal skin under different environmental conditions, ,qcta Dermatovener, 51, 111-119. 1971. (9) R. Scheuplein and L.J. Morgan, "Bound water" in keratin membranes measured by a microbalance technique, Nature 214, 456-458, 1967. (10) G. R. Berube, M. Messinger and M. Berdicke, Measurement in vivo of transepidermal moisture loss, .]. $oc. Cosmet. Chem., 22, 361-368, 1971. (11) F. A. F. Thiele and D. A. Realy, Conference Soci•t• Francaise de Dermatologie et de Syphilligraphie, 10 Mai 1975, Besancon, France. (12) K. A. Grice and F. R. Bettley, Skin water loss and accidental hypothermia in psoriasis ichtiosis and erythroderma, Bri. Meal..]., 4, 195-198, 1967. (13) I. Weil and H. M. Princen, Diffusion theory analysis of transepidermal water loss through occlusive films,.]. $oc. Cosmet. C/•em. 28, 481-484, 1977. (14) E. R. Cooper and B. F. Van Duzee, Diffusion theory analysis of transepidermal water loss through occlusive films,.]. $oc. Cosmet., 27, 555-558, 1976. (15) R. L. Anderson, J. M. Cassidy, J. R. Hansen and W. Yellin, The effect of in vivo occlusion on human stratum comeurn. Hydration - dehydration in vitro,.]. Invest. Derm., 61,375-379, 1973. (16) E.J. Clar, C. P. Her and C. G. Sturelle, Skin impedance and moisturization, Conf. of the Society of Cosmetic Chemists of Great Britain, 1974.

TRANSEPIDERMAL WATER LOSS 343 (17) R. M. Handjani, B. Rondot and F. Lachampt, Perspiratio insensibilis controled by specific associations of lipids. Cosmet. Perf., 90, 39-41, 1975. (18) R. M. Handjani, B. Rondot and F. Lachampt, Measurements of the moisturizing effect, Cosmet. Toiletries, 91, 25-30, 1976. (19) J. D. Middleton, The mechanism of action of sufactants on the water binding properties of isolated stratum corneum,J. Soc. Cosmet. Chem., 20, 399-412, 1969.