Not only are they more likely to burn when the mercury rises, but they also feel the most pain when it drops.

Researchers at Louisville University in Kentucky have discovered that people with ginger hair are more sensitive than most. A study released yesterday shows that the presence of a ginger gene means many redheads need extra doses of anaesthetic during surgery because they suffer pain more acutely.

Scientists compared the pain tolerance of 60 ginger-haired volunteers with 60 brunettes. The redheads began to feel pain at around 6C (43F), unlike the volunteers with dark hair, who did not really begin to flinch until the temperature got down to freezing.

Researchers think that the ginger gene, known as MC1R, may cause the temperature-detecting gene to become over-activated, making redheads more sensitive to the cold. It is hoped that this research can be used to develop better pain-relieving drugs and anaesthetics.

Daniel Sessler, the director of the university's outcomes research institute and department of anaesthesiology, said the study had confirmed anecdotal evidence that redheads were more sensitive to certain types of pain.

"After a previous study we received more than 100 communications from redheads who claimed that anaesthesia often failed or that unusually high doses of local anaesthetics were required to achieve adequate analgesia," he said. "It suggested that the redhead gene may have some role in the pain pathway. That redheads are subject to sunburn and skin cancer must be linked to the difference in pain sensitivity."

Vanessa Collingridge, a red-headed television presenter and author, said: "I am like a reptile because I am so cold-blooded. I have caught hypothermia twice while filming in Scotland - and that was during the summer. Redheads are known for having lower pain thresholds and my midwife even warned me when I was giving birth to my son Archie. I usually need a double dose of anaesthetic when I go to the dentist."

Simon Cheetham of Red and Proud, a website that claims to represent redheads, welcomed the research, but said it shattered the myth of the tough, ginger Scottish male.

"The stereotype of a Celt is a wild, kilted man with red hair who takes no notice of the temperature," he said. "In fact most redheads don't really like extremes of temperature."