Iontophoresis primarily uses direct current. This method involves the application of a continuous electrical current to the skin, which facilitates the transdermal delivery of ionic substances. The direct current creates a uniform flow of electricity, allowing charged particles to migrate through the skin’s barrier. This characteristic is essential for effective iontophoresis, as it ensures that the medication or solution is driven into the tissues in a controlled manner.
In contrast, alternating current reverses direction periodically, which would not provide a stable environment for the delivery of ions. High frequency current, while useful in various skin treatments, operates on a different principle and does not penetrate the skin in the same way as iontophoresis does. Pulsed current, although it does have its applications in electrotherapy, also does not lend itself well to the continuous, steady application needed for effective iontophoresis.
Thus, the correct answer reflects the fundamental principle behind iontophoresis, making direct current the appropriate choice for this method of treatment.