A chemical from chilli peppers may be able to kill pain without affecting touch or movement.
This might in theory mean a woman in labour could have an epidural without losing the ability to move her legs, or the sensation of her baby being born. Conventional local anaesthetics affect all nerve cells.
But the researchers Harvard team, writing in Nature, said that with capsaicin, the chilli chemical, they can target just pain receptors.
However, a UK expert said it might be difficult to inject it safely.
Numbness is actually a side-effect of the pain-killing properties of local anaesthetics - caused when the drug blocks signals not only from the nerve endings which cause pain, but other nerve endings which simply detect the sensation of touch.
And when anaesthetic "blocks", are injected into the spine, they can interfere with other nerves, causing temporary paralysis - such as that felt in the lower limbs after an epidural injection.
Source - BBC