A transcutaneous electrical nerve stimulation (TENS) unit is a battery-operated device that some people use to treat pain. TENS units work by delivering small electrical impulses through electrodes that have adhesive pads to attach them to a person’s skin. These electrical impulses flood the nervous system, reducing its ability to transmit pain signals to the spinal cord and brain. The same electrical impulses also stimulate the body to produce natural pain relievers called endorphins. In this article, learn more about the uses of a TENS machine and the research on its effectiveness.