Iontophoresis is a non-invasive method of propelling high concentrations of a charged substance, normally medication or bioactive agents, transdermally by repulsive electromotive force using a small electrical charge applied to an iontophoretic chamber containing a similarly charged active agent and its vehicle. To clarify, one or two chambers are filled with a solution containing an active ingredient and its solvent, termed the vehicle. The positively charged chamber, termed the anode will repel a positively charged chemical, while the negatively charged chamber, termed the cathode, will repel a negatively charged chemical into the skin.
Source: Wikipedia