However, stimulating the sense of smell only seems to work for women.

I would bet that good odours would help in reducing clinical pain, augment mood and then help in the healing process

Dr Serge Marchand

Dr Serge Marchand and Dr Pierre Arsenault at the University of Qu�bec in Abitibi-T�miscamingue asked 20 men and 20 women to keep their hand immersed in painfully hot water for as long as they could while smelling various odours.

New Scientist magazine reports that when given pleasant aromas such as almond extract to sniff, the women experienced significantly less pain.

Foul smells such as vinegar seemed to slightly intensify their pain.

However, the pain felt by the men was not affected by the smells.

Perception

Both sexes reported feeling happier in the presence of good smells, while bad smells put them in a worse mood.

But the researchers say that this effect on the emotions cannot be what changed the women's perception of pain. If it was, the men should have responded in the same way.

Women are typically more sensitive to odours than men.

But this also cannot explain why only women feel the pain-relief benefits, because the women in the study didn't rate the intensity of smells differently from the men.

Pleasant sensations of touch are known to activate an area of the brain's frontal cortex used for taste and smell.

So it is possible that smells could be altering the sensory processing of touch, pain and temperature by affecting this part of the brain in women.

Dr Marchand told BBC News Online that it was possible that women had a heightened response to smells because they were biologically programmed to recognise and react to the odours of their own babies.

He said: "It would need more research to be sure, but I would bet that good odours would help in reducing clinical pain, augment mood and then help in the healing process."

Little understanding

Dr Beverly Collett, a pain management consultant at University Hospital Leicester and president-elect of the Pain Society, said the way that pain was perceived is still little understood.

She said: "We do know that pain perception is different between men and women. It may be due to some sort of genetic difference, or it may be that it is something to do with learned behaviour.

"Women tend to have a lower pain threshold, and a lower tolerance of pain.

"They also tend to respond differently to analgesic drugs used in clinical practice. For instance, morphine tends not to be quite as effective at relieving pain in woman as it is in men."