Relation of electrical properties of skin to structure and physiologic state

Interpretation of cutaneous electrical measurements in terms of structure or function requires special techniques for identifying the separate contributions of the various elements. Resistance measures have different implications depending upon whether the subject is sweating and whether the electrode preparation is wet or dry. Microelectrode measurement indicates that the stratum corneum and other epidermal layers represent a significant pathway for ion conductance. Impedance measurement allows estimation of skin capacitance and of the thickness of the capacitative element. When applied to data on excised stratum corneum, this analysis indicates the presence of a relatively impermeable layer less than 2 microns thick, a conclusion subject to some doubt because of uncertainty over the dielectric constant of wet keratin. The use of impedance measurement with closely spaced electrodes gives an indication of the hydration of the superficial horny layer and also demonstrates reabsorption of sweat from this region. Potential measurement at the surface reflects the relative internal resistance of two parallel sources, the sweat glands and an "epidermal generator."