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.
Certainly the idea of 5 cc of Tabasco shot into your ham sounds excruciating.