Red Hair Gene

People with red hair are often said to need more anaesthetic, a claim that rests largely on a study of twenty women.¹

A larger study of patients undergoing surgery later found no difference in how red-haired people responded.²

The original study was published in 2004 by E. B. Liem and colleagues, with D. I. Sessler as senior author.¹ They anaesthetised ten women with bright red hair and ten with dark hair using the inhaled anaesthetic desflurane, then applied a painful electrical stimulus and raised or lowered the dose depending on whether each woman moved.¹ The red-haired women needed an average concentration of 6.2 per cent against 5.2 per cent for the dark-haired group.¹ Nine of the ten redheads carried two altered copies of MC1R, the melanocortin-1 receptor gene, mutations of which are common in people with red hair.^{1, 2} The authors concluded that red hair is a distinct phenotype linked to a higher anaesthetic requirement.¹

A second study by the same group in 2005, of thirty women in each group, found that redheads were more sensitive to cold and heat pain but no more sensitive to electrical pain.² The local anaesthetic lidocaine, injected under the skin, was less effective in them.²

In 2012 P. S. Myles and colleagues in Australia followed 468 adults having planned surgery under general anaesthesia.^{2, 3} Red-haired patients did not differ from others in recovery time, pain scores or quality of recovery, and after adjusting for age, sex, health and the length of anaesthesia there was no difference in the time they took to open their eyes.² A 2013 study by the original research group found no difference in the dose of the intravenous anaesthetic propofol needed by red-haired women.³

A 2014 evidence review by the health department of the Region of Murcia in Spain concluded that there was no evidence that hair colour affects anaesthetic requirements or response.² The anaesthesiologist Christopher O'Connor reached the same conclusion in 2019.³

Twenty volunteers produced a striking result. The larger studies that followed have not repeated it.