As the authors of a recent study published in BMJ attest, society’s red-haired members don’t always get a fair shake. Hoary stereotypes, such as the idea that redheads are also hot heads, are mixed together with actual physiological differences — such as a heightened sensitivity to pain. Now science is getting a better understanding of redheaded physiology than ever before.

In numerical terms, people with red hair are a decided minority. They comprise just 2-6% of the population of the northern hemisphere and 1-2% worldwide. It’s genetics that make them such rare birds. (More on Time.com: How to Keep Surgeons From Leaving Things Behind)

The carrot-top coloration is caused by a gene on chromosome 16 that affects the melanocortin-1 receptor (MC1R) protein, which often leads to the redheads’ characteristic pale skin and light eyes, as well as a sensitivity to ultraviolet light — which is why they must slather on the sunscreen when they go outside. Because the gene is recessive, both parents must carry it in order for a red-haired child to be born. That’s not difficult — 80% of the global population carries the redheaded gene even most if they do so invisibly. (More on Time.com: The Top 10 Redheads)

For those few who do have the redhead phenotype, the physical challenges go beyond the occasional sunburn — something that surgeons well know. And that’s what the BMJ authors sought to explore in their meta-analysis, or survey of the existing scientific literature

Operating room docs, for example, have long reported that redheads appear to need more anesthetic than others. The new study suggests that that observation is an accurate one — mostly. Those with the MC1R mutation are more sensitive to opiate pain killers — which means they’d actually need less — but less sensitive to other types, most notably lidocaine injections. One study which used heat-related pain as its litmus of overall sensitivity showed that redheads indeed felt things more acutely and unpleasantly, probably because the MC1R mutation releases a hormone that stimulates a brain receptor associated with pain regulation. (More on Time.com: Study: Researchers Identify Hundreds of Gene Variants That Contribute to Height)

Redheads are also said — anecdotally at least — to be more susceptible to hernias. The study did not establish that conclusively, but it did find a tangential link between chromosome 16 and a condition called brittle cornea syndrome, the sufferers of which have a slightly elevated hernia risk.

Less substantiated by the study was the belief that people with red hair are more susceptible to hemorrhages. A survey of tonsillectomy patients found that about 7% of both red-haired and control patients experienced post-surgical bleeding. And in a study of the blood coagulation of 50 women, half of whom were redheads, there was no difference in clotting.

Overall, the researchers concluded that even if redheads require a little extra handling on the operating table, trepidation among surgeons had more to do with stereotypes than with clinical evidence.”It would seem that the reputation of people with red hair for having increased perioperative risk is without any basis in fact and should only be used as an excuse of last resort by surgeons defending problematic bleeding or recurrent hernias,” concluded authors, Andrew L Cunningham and Christopher P Jones. Take that, blonds and brunettes!

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