Changes in the electrical properties of the skin outermost layer during pulse electrotreatment

The kinetics of changes in the electric current I(t) passing through human skin samples of full thickness in vitro during rectangular voltage pulses (amplitude, 10-60 V; duration, 5-8 ms) was investigated. The function I(t) was shown to rapidly decrease, to pass through its minimum, and then to increase slowly. With the increase in voltage, the minimal current grew; the dropping branch became less pronounced (up to its complete disappearance at 40 V); and the position of the minimum shifted to short times. All these features of the current response were explained in the assumption that the electrical properties of the skin at a voltage less than 30 V are determined by macropores of skin appendages (hair follicles, sweat glands, etc.). The dropping branch of the current was a superposition of the charging current of the macropore wall capacity and the conductive current through the electroporated walls. At voltages over 30 V, increases in current and conductivity are determined by electroporation of the lipid-corneocyte matrix of the skin outermost layer (stratum corneum). The kinetics of skin resistance restoration after pulse electrotreatment was also investigated. The characteristic time of restoration, which did not exceed 1 min at 10 V, increased up to dozens of minutes at voltages above 30 V. The investigated phenomena were found to be very much similar to the electroporation of plane lipid bilayers and plasma membranes of isolated cells.