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Red hair in close-up (Image via Wikipedia)I’ve recently come across some press coverage reporting research by Danish scientists which has shown that “redheads feel pain differently than the rest of us”.  I read the paper and thought it would be nice to write something short about it here, both for the change of tone and to give my own perspective on it.

Natural red hair is usually due to  a gene called melanocortin 1 receptor (MC1R); according to Wikipedia, redheads make up about 1-2% of global population with the highest concentration (13%) being found in Scotland.  Redheads have a defective form of MC1R, resulting in an increased proportion of the yellow/red pigment phaeomelanin  compared with the brown/black eumelanin.  This results in the person having red hair, light skin and an increased sensitivity to UV radiation.  It’s thought that red hair was able to become more common in humans who migrated out of Africa because they experienced less selection against the mutant form of MC1R; once the negative selection was relaxed, it’s possible that factors like mate choice may have created some frequency dependent selection to maintain or increase the mutant MC1R frequency.

The study, published last year in the Scandinavian Journal of Pain, looked at the sensitity of redhead vs. non-redhead females to different kinds of pain stimulus.   As the study acknowledges, the idea that redheads have a different pain response is hardly new.  There have been several previous studies with variable results.  Redheads have been found to be more sensitive to heat or cold but less sensitive to electrical stimulation; they also seem to be resistant to some kinds of painkillers (requiring a higher dosage for the same effect) but more sensitive to other kinds.  This variability probably just reflects the fact that pain perception is a relatively complicated field — our bodies responded to different kinds of painful sensations in different ways and MC1R might be involved in different ways in some or all of these responses.

The researchers exposed the arms of 20 redhead and 20 non-redhead females to gradually increasing heat or pressure; the participants were told to press a button when they reached their pain tolerance threshold.  Although only females were used in these experiments, that seems to have been simply to minimize variation; there’s no reason to expect that the results would be different for males.  In addition to testing the direct pain response, the researchers also checked for secondary changes in sensitivity resulting from an initial pain treatment.  After treating an area with heat and the chemical capsaicin (which is what makes chili hot), a pinprick was used to check for increased pain sensitivity (hyperalgesia) and a soft brush was used to check for a painful response to a non-pain stimulus (allodynia); both kinds of increased sensitivity are probably familiar from your own experience with, for example, sunburn.  The pinprick or brush started on “normal” skin and were moved closer to the injured area until the subject reported a clear change in sensation.

This study didn’t find any difference in redheads’ tolerance of heat or pressure; however, the redheads did have a smaller area of response to the pinprick (but not the brush) after heating & capsaicin treatments.  In other words, the only difference found in this study was that after a pain stimulus (such as a burn) redheads have a smaller area of increased sensitivity to painful stimuli.  As I said earlier, this has generally been reported as “redheads respond differently to pain”; while that might be technically true, it also seems to be quite a strong statement based on this work — after all, there was no difference in redheads’ response to heat or pain.  I don’t mean this as a disparagement of this work, which generated novel results that may well have important clinical usage.  On the contrary, I want to draw attention to the fact that coverage of this research seems to have ignored some important results.  Research results are not always straightforward and often have to be interpreted within a context; reporting which trades this nuance for marketability does a disservice to both the reader and the researcher.  Addressing this problem has been part of my motivation for getting involved in science writing.

To be honest, I also think that reporting which simply lumps this research on top of our cultural baggage about redheads is missing an opportunity to say something more interesting.  To me, the interesting part of this research (in this and earlier studies) is the link between MC1R and pain response.  It’s a wonderful example of the fact that a gene rarely has a single, simple effect; each gene can play different roles in lots of different pathways (like hair colour and pain perception), each of which is itself a complex interaction of many different parts.  The really interesting story is about how these different layers of complexity can produce effects which are qualitatively similar while actually being different for every single individual.  Redheads don’t feel pain differently from the rest of us; each of us (and every other living thing) experiences pain in our own way, along with a host of other sensations.  This layered complexity is an inescapable aspect of biology, generating the cornucopia of systematic diversity which is the source of its enduring allure.

Ref: Andresen, T., Lunden, D., Drewes, A., & Arendt-Nielsen, L. (2011). Pain sensitivity and experimentally induced sensitisation in red haired females Scandinavian Journal of Pain, 2 (1), 3-6 DOI: 10.1016/j.sjpain.2010.08.005

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