Transcutaneous electric nerve stimulation (TENS) uses electrical fields to directly affect pain transmission. Cutaneous nerve fibers are stimulated using surface electrodes emitting a mild electrical current. High-frequency low-intensity stimulation patterns typically lead to immediate pain relief, while low-frequency, high-intensity patterns typically lead to longer-lasting relief but is less well-tolerated. Mechanisms of pain relief from TENS is thought to include modulation of gating mechanisms at the dorsal horn system which decreases pain transmission to the brain, stimulation of endogenous neurotransmitters, including endogenous opioids.