Iontophoresis is a physical process in which ions flow diffusively in a medium driven by an applied electric field. Iontophoresis is to be distinguished from the carriage of uncharged molecules by diffusive fluxes of other molecules, especially of solvent molecules, for example by electro-osmosis, that is to say by flux of uncharged solvent molecules carried as a cross-effect of iontophoresis. These phenomena, directly and indirectly, constitute active transport of matter due to an applied electric field. The transport is measured in units of chemical flux, commonly µmol/cmh. The transport of a charged species of interest may also be measured in terms of a representative electric current, but that current might not be the whole of the current driven by the applied electric field.