MICROWAVE DIELECTRIC ANALYSIS OF HUMAN STRATUM-CORNEUM IN-VIVO

The dielectric properties of the human skin stratum corneum (SC) in th e frequency range higher than 10(7) I-fz are not well understood becau se of the difficulty in selective scanning of the SC area in vivo. The present study was carried out to make clear factors responsible for t he dielectric properties using a measuring system specially developed for the study of SC [S. Naito, M. Hoshi, S. Mashimo, Anal. Biochem. 25 1 (1997) 163-172]. We found that the dielectric properties of SC can b e expressed by the linear combination of two relaxation processes and d.c. conduction. The faster relaxation is that of free water. The slow er relaxation and d.c. conduction were analyzed using a model assuming interfacial polarization between dissimilar materials. We concluded t hat the polarization is the origin of the slower relaxation process be cause the experimental data could be well interpreted according to the above mechanism. We also concluded that the polarization of swelled S C locates at the interface between SC cells and the intercellular lipi d layer, or at the interface between the lipophilic and the hydrophili c part of the lamellar structured intercellular lipid layer. (C) 1998 Elsevier Science B.V. All rights reserved.