WASHINGTON: A new approach to anaesthesia using the chemical that gives chilli peppers their kick promises an improved way to treat pain in surgery, dentistry and childbirth, researchers said on Wednesday.

Current local anaesthetics deaden all nerve cells and not just the pain-sensing ones, causing temporary paralysis and numbness. That's why dental patients after a root canal, for example, may leave their dentist's office drooling, with a numb mouth and some muscles temporarily paralysed.

Now, researchers have found a way to target only the pain-sensing nerve cells while avoiding the neurons responsible for muscle movement or sensations such as touch. They demonstrated the approach in rats and feel confident it will also work in people.

They gave the rats injections containing capsaicin, the active ingredient in hot peppers, and a derivative of the common local anaesthetic lidocaine. Working in concert, these chemicals targeted pain-sensing neurons, stopping them from transmitting "ouch" signals to the brain.

The rats were placed on an uncomfortable heat source and had their paws pricked, but showed no signs of feeling pain and moved and behaved normally. The injections took effect within half an hour, and the pain relief lasted for several hours.

The researchers think this approach could be useful in dental procedures like tooth extractions, knee surgery and other joint operations, for women during childbirth and potentially for chronic pain.