Characteristics of skin admittance for dry electrodes and the measurement of skin moisturisation

The properties of skin adminttance were investigated with the intention of applying them to skin moisturisation measurement. Skin admittance is determined by measuring relative permittivity and the resistivity of the stratum corneum, and by contact ratio between dry electrode and stratum corneum. It was found, however, that the contact ratio is the predominant factor producing the change of skin admittance induced by changes in the water content of skin. To measure skin admittance, the following conditions were found to be approriate: (a) frequency of about 100 kHz; (b) concentric electrodes, the diameter of the measuring (inner) electrode being about 5 mm, and (c) an electrode pressure of about 100 g cm−2. Based on these optimal conditions, a system for measuring skin admittance was constructed. All measuring procedures were automated. Experimental observations made with this system have indicated its usefulness for the measurement of skin moisturisation.