Interferential current ( IFC) originated to overcome the problems of skin resistance. The biological frequency of human cells occurs in the range of .1 - 200 Hertz, or pulses per second ( pps). This simply means that in order to effect biological changes in cells the pulses that cause that change occur between the two pulse rates identified previously.
The problem that exists is the cells that a clinician is trying to affect lie below the surface of the skin, so the current has to penetrate through the skin prior to arriving at the targeted cells. Herein lies the problem.
Typical values of skin resistance for an area of 100 sq. cm is 3,000 ohms when one applies an alternating current of 50 Hz. Now if one increases the hertz, pulses per second, to 5,000 pps the resistance drops dramatically from 3,000 ohms to only 40 ohms. This is great but now the frequency of 5,000 is outside the biological frequency of the cells themselves.
Interferential is simply the application of two currents of 4,000 pps to lower the resistance and then one of the two currents actually has 4,0001 up to 4,250 pps. The 4,000, or if two channels being used then 8,000 pps, are there only to reduce the resistance so a biologically active current can be administered to the underlying cells for therapeutic results.
Further understanding of this phenomena can be found on the blog by Dr. Giovanni De Domenico, "Askdrgion".