ABSTRACT
Since the early 1970’s the electrical properties of keratins have been known to highly depend on their water content. When dry, keratins are quite good insulators, whereas when wet, or merely not dry, they exhibit a certain transport of the electrical charges (electron, proton, ion, etc.) through their structure (1). A former paper illustrates this change in behavior of the human stratum corneum (SC): human SC conductance in the dry state is of 4 orders of magnitude lower compared to that in the humid state (2). This is the reason why capacitance and/or conductance methods are today so commonly used for measuring water content of the SC (3). These methods provide relative values that are linked to the skin water content, and yet very little information is available regarding the precise location and distribution of water in skin layers. Another difficulty comes from the fact that skin is not flat, so applying a hard electrode to its surface does not permit to get the actual value of the measured electrical property. However, these methods are really convenient for developing efficient cosmetics and they are widely used. The rather new “capacitance imaging” (CI) method does not solve all the above-mentioned problems, but due to the ability to view the skin surface water content, it allows this phenomenon to be studied comprehensively.
