418 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS REFERENCES (1) N.J. Harrick, Surface study in semi-conductors by frustrated total internal reflection, Ann. N.Y. Acad. Sci., 101,928-959 (1963). (2) J. Fahrenfort, Attenuated total reflection: A new principle for the production of useful infrared spectra or organiz compounds, Spectrochim. Acta, 17,698-709 (1961). (3) N. A. Puttnam and B. H. Baxter, Spectroscopic studies of skin in situ by attenuated total reflectance, J. Soc. Cosmet. Chem., 18, 469-472 (1967). (4) M. Gloor, G. Hirsch and H. Willebrandt, On the use of infrared spectroscopy for the in vivo measurement of the water content of the horny layer after application of dermatologic ointments, Arch. Dermatol. Res., 271,305-313 (1981). (5) R. Osberghaus, C. Gloxhuber, H. van Raay and S. Braig, Hydagen F, ein neuer Hautfeuchtigkets- regulator--Methoden und Ergenbnisse des Wirkungsnachweises,.J. Soc. Cosmet. Chem., 29, 133-146 (March 1978). (6) J. B. Dawson, D.J. Banker, D.J. Ellis, E. Grassam, J. A. Cotterill, G. N. Fisher and J. w. Feather, A theoretical and experimental study of light absorption and scattering by in vivo skin, Phys. Med. BioL, 25,695-709 (1980). (7) V.J. Anselno and B. E. Zawacki, Diagnosis of cutaneous thermal burn injuries by multispectral imaging analysis,JPL Publication, 79-34 (September 1978). (8) R. V. Dent, The photographic aspect of light reflection from human skin, J. Lab. ½lin. Med., 26, 1852-1862 (1941). (9) A.J. Quattrone and K. Laden, Physical techniques for assessing skin moisturization, J. Soc. Cosmet. Chem., 27, 607-623 (1976). (10) N. A. Puttnam, S. Lee and B. H. Baxter, Application of attentuated total reflectance IR spectroscopy to toilet articles and household products. I. Qualitative analysis, J. Soc. Cosmet. Chem., 16, 607-615 (1965). (11) N. A. Puttnam, Attenuated total reflectance studies of the skin, J. Soc. Cosmet. Chem., 23, 209-226 (1972). (12) R. E. Baler, Non-invasive rapid characterization of human skin chemistry in situ, J. Soc. Cosmet. Chem., 29, 283-306 (May 1978). (13) M. Gloor, V. Willebrandt, U. Thomer and W. Kupferschmid, Water content of the horny layer and skin surface lipids, Arch. Dermatol. Res., 268, 221-223 (1980). (14) R.J. Scheuplein, A survey of some fundamental aspects of the absorption and reflection of light by tissue,J. Soc. Cosmet. Chem., 15,111-122 (1964). (15) W. P. Ferren, MIR infrared spectroscopy in skin analysis, Am. Perf Cosmet., 84, 27-36 (December 1969). (16) R.J. Marshall and R. Marks, A photographic method for the measurement of skin surface textures, Bioengineering and The Skin, 4, 7-15 (July 1982).

j. Soc. Cosmet. Chem., 34, 419-428 (December 1983) Impedance methods for studying skin moisturization J. L. LEVEQUE and J. DE RIGAL, DJpartement de Physique, Laboratoires de Recherche de L 'OrJal, I, Avenue de Saint-Germain, 93601 Aulnay- sous- Bols, France. Received September 1983. Presented at the IFSCC/SCCJoint Conference on Skin, San Francisco, September 1983. INTRODUCTION For the last several years the primary claim for skin cosmetics has been moisturization. This complies, on the one hand, with the desires of consumers who confusedly associate moisture and good skin condition. On the other hand, it corresponds to an objective reality since we now know to what extent water is capable of modifying all the physical properties of the stratum corneum (SC), the elected target of cosmetic treatments. For a physicist keratin is, above all, a dielectric medium, that is, a medium of weak electrical conduction. This is especially true when the keratin is dry. When the keratin is moisturized, the situation is somewhat changed, since the water molecule, because of its very strong dipolar character, combines very readily with the keratin chains and, thus, makes them more sensitive to the electrical field. In fact, the skin and, more precisely, the SC is sensitive to the effects of an applied electrical field. At least three types of mediating structural components may be involved: keratin chains, which have a dipolar moment (Figure 1), are made more movable by the plasticizing effect of water ions, in the intercellular spaces, can react to the application of an electrical field and even, to a certain extent, move with it if their mobility is sufficient, that is, if the viscosity of their environment permits it (1) (Figure 2) water molecules themselves are able to form a continuous network of hydrogen bonds allowing the exchange of a proton between two radicals of the type OH 3 and OH (Figure 3). These three mechanisms illustrate how the water molecule, either directly or indirectly, acts upon the electrical properties of the SC. There are thus good reasons for selecting electrical methods for the study of moisturization of a medium that is itself only slightly conductive. 419