People with red hair are more sensitive to pain and consequently need more anaesthetic during operations than other patients, according to new research.

“Red hair is the first visible human trait, or phenotype, that is linked to anaesthetic requirement,” says anaesthesiologist Edwin Liem, who conducted the research at the Outcomes Research Institute of the University of Louisville, US.

Ten red-haired women between 19 and 40 years of age and ten more with dark hair were given a commonly-used inhaled anaesthetic in the study. After each dose of the anaesthetic, the women were given a standard electric shock.

The process was repeated until the women said they felt no pain. Their reflexes were also monitored to assess the effectiveness of the painkiller. The researchers found that red heads required 20 per cent more aesthetic to dull the pain.


Pain threshold

In people with red hair, the cells that produce skin and hair pigment have a dysfunctional melanocortin 1 receptor. Liem says this dysfunction triggers the release of more of the hormone that stimulates these cells, but this hormone also stimulates a brain receptor related to pain sensitivity.

Liem is hopeful that the research will lead to improved patient care. Anaesthetists must be very careful when choosing how much anesthetic to give a patient before an operation. Too little and the patient could wake up, too much and they could suffer cardiac complications.

The research will also move forward understanding of the relationship between genetic characteristics and anaesthetic requirements, he says: “Investigating the role of melanocortin system in the central nervous system is likely to help us understand fundamental questions such as which systems in the brain produce unconsciousness and which modulate pain perception.”

The research is being presented at a meeting of the American Society of Anesthesiologists on Tuesday 15 October.