The first uses of electroanalgesia were recorded by Aristotle, Pliny
and Plutarch, who reported application of electrical fish to pain sites.

The neurophysiological basis of the analgesic action of TENS remains under investigation, yet there are two popular theories  to explain how TENS successfully decreases or eliminates pain.

• The Gate Control Theory is the most commonly advanced explanation, suggesting that by electrically stimulating sensory nerve receptors, a gate mechanism is closed in a segment of the spinal cord, preventing pain-carrying messages from reaching the brain and blocking the perception of pain.

• The Endorphin Release Theory suggests that electrical impulses stimulate the production of endorphins and enkaphalins in the body. These natural, morphine-like substances block pain messages from reaching the brain, in a similar fashion to conventional drug therapy, but without the danger of dependence or other side effects.