One of the main benefits of interferential is that the stimulus itself overcomes the resistance of the skin so the subcutaneous tissues can be reached.  There are methods one can use to decrease the resistance and thus increase the efficacy of the treatment.
Prior to treatment one may.... wash the treatment area in hot water.  The heated water will produce a faster blood flow to the area as the blood is trying to move the heat away and have the treatment area come into homeostasis with the surronding tissues.  This increased blood flow now provides blood closer to the skin surface and blood itself is a conductor of electricity.  This increase will allow greater ability to stimulate the nerves in the area.  Also the use of water on the skin is very good as the skin when dry is not conductive but once the area is wet then it allows less resistance and greater conductance on the surface.  The water will permeate into the uneven skin surface area, eliminating air ( resistor ), and allow for a more even conductive area and greater distribution in the affected area.

    The combination of hot water providing conducatance and the advance of blood into the subcutaneous tissues will enhance the overall effect of interferential treatment for the patient.