Researchers in Britain say that the old fashioned idea that heat relieves pain does have some truth in it and hugging a hot-water bottle can have a similar effect to a painkiller.
Scientists at University College London (UCL) have found by using DNA technology to monitor heat and pain receptors within cells, that temperatures over 40C (104F) switch on internal heat receptors which block the effect of chemical messengers that cause the body to detect pain.
Dr. Brian King, of UCL who led the research says they were interested in testing the theory that heat relieved internal pain such as period cramps and colic.
The team used DNA technology to make both heat and pain receptor proteins in the same cell and then observed the molecular interactions between the heat receptor TRPV1 and the P2X3 pain receptor.
They found that heat does not just provide comfort and have a placebo effect but the heat receptor can also block the pain receptor.
This pain message is apparently activated by ATP, a chemical that pours out of cells when they are damaged and by blocking the pain receptors, TRPV1 is able to stop the pain being sensed by the body just as a painkiller does.
Dr. King says the molecular data showed heat could relieve pain for up to an hour.
He says 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.
Dr. King says the focus of future research will continue to be the discovery and development of pain relief drugs that will block these P2X3 pain receptors which are the key to the development of drugs that will alleviate debilitating internal pain.
Dr. King hopes his discovery will lead to new pain-relief drugs that could reduce the need for opiates such as morphine.
The research was presented to the Physiological Society conference.