People with red hair are more susceptible to pain, according to doctors.

Research carried out in the United States suggests that redheads need 20% more anaesthesia than people with other hair colour.

Doctors believe that genes which are responsible for red hair also have a role in managing pain.

In a nutshell, redheads are likely to experience more pain

Dr Edwin Liem

They said the findings could have important implications for patients who are undergoing surgery.

Dr Edwin Liem, of the University of Louisville in Kentucky, studied the effects of an inhaled anaesthetic called desflurane on women between the ages of 19 and 40.

Reflex movement

Their physical responses to the drug were closely monitored. In particular, Dr Liem looked out for unconscious reflex arm or leg movements in response to painful stimulation.

He found that women with red hair needed more of the drug to stop these reflex movements compared to those with dark or blond hair.

"In a nutshell, redheads are likely to experience more pain from a given stimulus and therefore require more anaesthesia to alleviate that pain," he said.

Dr Liem said the findings could be explained by genetics, and in particular variations in the melanocortin 1 receptor which is linked to red hair.

He said the discovery could help scientists to find out more about how the body manages pain.

"Since red hair can be traced to particular mutations in the melanocortin 1 receptor, we now have the opportunity to evaluate central nervous system pathways that may influence or mediate anaesthetic requirement," Dr Liem said.

"Investigating the role of melanocortin system in the central nervous system is thus likely to help us understand fundamental questions such as which systems in the brain produce unconsciousness and which modulate pain perception."

He added: "Red hair is the first visible human trait, or phenotype, that is linked to anaesthetic requirement."

Dr Liem said scientists do not fully understand how anaesthesia works but suggested that this latest study could offer clues.

"The art and science of anaesthesiology is choosing the right dose," he said.

"There is very little difference between the effective dose and the toxic dose of most anaesthetics.

"Patients can awaken during surgery if they are given insufficient anaesthesia or suffer cardiac and pulmonary complications when they are given too much."

The findings were presented to a meeting of the American Society of Anesthesiologists in Orlando, Florida.