Electrical properties of skin at moderate voltages: contribution of appendageal macropores.

The electrical properties of human skin in the range of the applied voltages between 0.2 and 60 V are modeled theoretically and measured experimentally. Two parallel electric current pathways are considered: one crossing lipid-corneocyte matrix and the other going through skin appendages. The appendageal ducts are modeled as long tubes with distributed electrical parameters. For both transport systems, equations taking into account the electroporation of lipid lamella in the case the lipid-corneocyte matrix or the walls of the appendageal ducts in the case of the skin appendages are derived. Numerical solutions of these nonlinear equations are compared with published data and the results of our own experiments. The current-time response of the skin during the application of rectangular pulses of different voltage amplitudes show a profound similarity with the same characteristics in model and plasma membrane electroporation. A comparison of the theory and the experiment shows that a significant (up to three orders of magnitude) drop of skin resistance due to electrotreatment can be explained by electroporation of different substructures of stratum corneum. At relatively low voltages (U < 30 V) this drop of skin resistance can be attributed to electroporation of the appendageal ducts. At higher voltages (U > 30 V), electroporation of the lipid-corneocyte matrix leads to an additional drop of skin resistance. These theoretical findings are in a good agreement with the experimental results and literature data.