The effects of electric current applied to skin: A review for transdermal drug delivery

Abstract Electrical enhancement of transdermal drug delivery is limited by undesired side-effects, such as tissue damage and pain. To aid in the development of electrical protocols which safely increase transport across skin, this review discusses the effects of electrical current on: skin electrical properties; sensation, pain, and muscle stimulation; and safety considerations. Quantitative relationships are presented whenever possible. First, the magnitudes and time scales of electrically induced changes in skin's electrical properties are characterized empirically and mechanistically. Then, sensation, pain, and muscle stimulation caused by electric current are each described as functions of electrical parameters (e.g., current, pulse length, pulse rate), based largely on the Weiss-Lapicque strength/duration relationship for nerve stimulation. Finally, safety considerations are also discussed and quantified from the perspective of thermal burns, the heart, skin irritation, and long-term exposure to current. Electrical parameters and uses of existing electrical medical devices and procedures are also summarized.