Heating pads and hot water bottles have long been thought to remedy stomach aches or menstrual pain.
Now scientists have figured out how heat applied externally relieves internal pain.
"The pain of colic, cystitis and period pain is caused by a temporary reduction in blood flow to or over-distension of hollow organs such as the bowel or uterus, causing local tissue damage and activating pain receptors," explains Brian King of the University College London. "The heat doesn't just provide comfort and have a placebo effect—it actually deactivates the pain at a molecular level in much the same way as pharmaceutical painkillers work."
When heat over 104 degrees Fahrenheit (40 Celsius) is applied to the skin, heat receptors deeper down, where the pain is, are switched on. The heat receptors in turn block the effect of chemical messengers that cause pain to be detected by the body.
Specifically, King and his colleagues discovered that a heat receptor called TRPV1 can block P2X3 pain receptors.
"The problem with heat is that it can only provide temporary relief," King said. "The focus of future research will continue to be the discovery and development of pain relief drugs that will block P2X3 pain receptors."
The study was presented yesterday at the annual meeting of the Physiological Society. It has not been published in a peer-reviewed journal.