Skin appendageal macropores as a possible pathway for electrical current.

The electrical properties of the outermost layer of skin are described by lipid-corneocyte (Zm) and appendageal (Za) impedance, which are connected in parallel. Appendageal macropores are considered as long tubes with distributed electrical parameters. It has been shown that not only Za, but also the macropore resistance Ra and capacitance Ca are frequency dependent. The input of Za in the overall impedance (Z) depends on the space density of active (conductive) macropores n(i), which increase with current density (i) and the duration of iontophoresis. Skin impedance has been demonstrated to decrease under the influence of iontophoretic treatment. Application of the theoretical model to these data provides an estimate of the increase in macropore density during iontophoresis. A comparison of these results with n(i), which was measured directly, shows a strong correlation supporting this unique model.