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How red hair impacts your anaesthesia requirement


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Having red hair affects your health and medical requirements in ways you may not aware.

According to an anaesthesiologist, Dr Daniel Sessler, in The New York Times, “it was essentially an urban legend in the anaesthesia community saying redheads were difficult to anaesthetise”. While an anecdotal impression is no proof, researchers took it upon themselves to actually come up with some data. A surprising amount of their findings point to an association between the gene mutation that results in red hair, fair skin, light eyes, and sensitivity to ultraviolet light, and a need for more anaesthesia than the rest of the population. Turns out some urban legends might be right.

Although about 80 per cent of the global population carries the recessive gene that results in red hair, only about two to six per cent of the northern hemisphere population has red hair. This number falls to one to two per cent worldwide. This is because two copies (from both parents) of the recessive gene are required to mutate the melanocortin-1 receptor gene (MC1R) leading to the red hair phenotype. This mutation causes elevated levels of a red pigment called pheomelanin and reduced levels of a dark pigment called eumelanin. People with darker hair may also have this mutation, but it is uncommon.

Currently, inhalational anaesthetic requirements are believed to be largely affected by age and body temperature and are exceptionally uniform in humans otherwise. Some studies have been able to show genetic factors to influence anaesthetic requirements in other animal species, like mice and fruit flies, so perhaps the same can be true for people?

Let's get to the research:

A 2004 study in anaesthesiology tested 20 white women with natural red or dark hair. The authors were able to show with high statistical significance that the anaesthetic requirement in people with red hair is increased by 19 per cent.

A 2005 study in anaesthesiology evaluated pain sensitivity in 60 red haired or dark haired women. The study showed that redheads were more sensitive to cold pain perception and had a lower tolerance. The local anaesthetic lidocaine, which is commonly used in dental practice, was also significantly less effective in redheads. The authors speculated that the gene mutation resulting in red-hair triggers the release of more of the hormone that stimulates a brain receptor related to pain sensitivity.

A 2009 observation study in The Journal of the American Dental Association genotyped blood samples of 144 individuals and surveyed them to measure general and dental-health anxiety. People with the MC1R gene reported significantly more dental care-related anxiety and were more than twice as likely to avoid dental care. The authors controlled for general anxiety.

There are other suspected clinical implications of the red-hair phenotype, like increased risk of haemorrhages, endometriosis, and hernias. The association between haemorrhages and endometriosis and red-hair has been studied but did not show significantly. An increased risk for hernias is possible but would be very difficult to prove.

Perhaps genetic factors play a role in anaesthesiology in ways of which we are not yet aware. The point is, we don't yet know and it might be very exciting to find out. If it isn't our curiosity driving us, it should be our desire to understand the human body better so that we can provide it with better care. Be it the MC1R gene mutation or other genetic factors, medicine could benefit from an improved understanding of their function.

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