This post is also available in Dutch.
Redhead meets dental surgeon. According to some scientists, that’s not a very attractive scenario. Redheads supposedly have a lower pain threshold than, say, blondes or brunettes. Is this true?
Recently, my wisdom teeth were removed by a dental surgeon. That would have been fine, if it wasn’t for the fact that I’m very sensitive to pain. Several times I have participated in experiments in which my neuroscientist-colleagues determine my pain threshold. In all cases it was reached rather quickly. Some research shows that redheads respond differently to pain, are more sensitive to certain painkillers, and need more anesthetic when undergoing surgery. So now the biologist in me is wondering how my red hair can possibly relate to my sensitivity to pain.
Redhead by genetic variation
According to researchers, approximately 80% of the people with red hair and fair skin have certain genetic variations in their MC1R gene (Melanocortin 1 Receptor). The MC1 receptor is an important protein for regulating our hair color and complexion, and it can mainly be found on pigment cells that produce melanin, the molecule responsible for the color of our skin and hair. Two important types of melanin are eumelanin, which is dark, and pheomelanin, which is red to yellow. Certain variations in this gene can cause less eumelanin and more pheomelanin to be produced. Often – but not always – this leads to red hair and fair skin that barely tans.
MC1 receptors in the brain
But MC1 receptors can also be found in the brain, where they don’t have anything to do with pigmentation. In the so-called periaqueductal grey, an area in the brainstem, MC1 receptors are present. This area is important for pain perception and contains – besides MC1 receptors – large quantities of opiate receptors. In this way, opiates such as morphine can relieve pain. The exact role of MC1 receptors in pain perception is not yet known.
Pain in redheads
One idea is that MC1 receptors can inhibit the effect of opiates in the brainstem. In people with genetic variations in their MC1-receptors, like many redheads, these receptors supposedly do not function as well. As a consequence, they experience less inhibition of opiates such as morphine and therefore better pain relief. This turned out to be the case in two studies investigating both mice and men. Those with genetic variations in their MC1 receptors indeed responded stronger to morphine. When it came to pain perception without pain relief, their pain threshold for different kinds of pain was higher than that of others with regular receptors.
However, it is also claimed that redheads have a lower pain threshold. That was shown by a study on dental pain and fear of dentists. Both measures were more intense for those with genetic variations in their MC1 receptors. In addition, it has been found that redheads are more sensitive to pain from hot and cold temperatures.
It seems that redheads do not necessarily have a lower pain threshold. But for some kinds of pain, it could be higher. Contradictory? Yes, but that nicely shows the complexity of pain perception, which involves both MC1 as well as opiate receptors (and many more!). So the link between red hair and pain perception definitely exists. The question of how exactly they relate to each other will require some more scientific research though.
Article on the most common genetic variation in redheads
Article on MC1-receptors, pain threshold and the effect of morphine
Article on fear for dentists and dental pain in redheads
Article on thermal pain