Evaluation of skin barrier function using direct current I: effects of conductivity, voltage, distance between electrodes and electrode area.

The objective of this study was to evaluate the reduction in skin barrier function caused by direct current iontophoresis by measuring resistance in the short term. The experiments were carried out using rat abdominal skin in vivo. The resistance was measured every 125 ms and analyzed using a two-compartment model consisting of surface and skin resistance. Moreover, the initial value and the rate constant of each resistance were calculated with the non-linear approximation program. The proposed method could evaluate the reduction in barrier function from the initial value and the rate constant of surface resistance with high sensitivity and accuracy. Using this proposed method, the effects of the conductivity of an adhesive pad, voltage, the distance between electrodes and the area of electrode were examined. The increase in conductivity of the adhesive pad decreased the initial value since the rate constant increased. The reduction in barrier function depends on voltage. Although the barrier function decreased up until an electrode distance of 1 cm, it increased beyond 1 cm. These phenomena contributed to the current pass portion in the skin because the resistance was in the order of the stratum corneum, epidermis and dermis. The initial value decreased with increasing electrode area. However, the rate constant was little affected since the current density of a topical electrode adjacent to the other electrode was high.