Skin impedance and moisturization

the in vivo evaluation of the HYDRATION state of STRATUM CORNEUM on human subjects are presented. The DIELECTRIC properties of HUMAN SKIN have been investigated over a wide range of frequencies (2 Hz-15 GHz). From stripping experiments it has been established that the low frequency IMPEDANCE (2 Hz-1 K_Hz) is located almost entirely in the HORNY LAYER. Skin impedance measurements have been carried out in relative humidity (rh)-controlled conditions using matched electrodes. An increase in the rh of the environment (at constant T o) causes an increase in the moisture content of the stratum corneum which is demonstrated by a decrease in impedance. The effect of MOISTURIZING ingredients can be demonstrated by comparison of impedance values before and after treatment with the ingredient in a convenient vehicle. Lasting and long-term effects are also assessed by measuring the time-course of the impedance value during the hours or days following a treatment. In skin not protected against dehydration, a decrease of the rh of the environment provokes an increase in the impedance. A BARRIER CREAM will act against dehydration, thus giving rise to a lesser increase in impedance. A procedure of testing protective creams is drawn from this experiment. A tentative interpretation of the relationship between hydration and skin impedance is proposed on the basis of the experimental results.