Redheads represent only 2% of the world’s population. What’s more, they feel pain differently than others. Researchers now know why.
There are probably more than 20 shades of red hair, but they all have the same genetic origin, a mutation in the MC1R gene encoding the melanocortin 1 receptor present in melanocytes.
In redheads, it is dysfunctional: it no longer recognizes melanocyte-stimulating hormone (MSH) and produces only one type of melanin, the pigment responsible for the color of skin, hair, and body hair, pheomelanin. The color of this pigment ranges from yellow to brown and is responsible for all shades of red.
But this is not the only consequence of this mutation. In fact, scientists have known for 15 years that mice and humans with the mutated MC1R gene feel pain differently than others. According to observations, redheads have a higher basal threshold of pain tolerance, or nociception, than others, and are more sensitive to opioid analgesics.
However, the mechanism underlying these findings remained unclear until now. A team of researchers from around the world has now discovered the not-so-obvious link between red hair and pain tolerance.
Explanations for the higher pain tolerance of redheads
In these experiments, which were conducted on red-haired mice with the mutated MC1R gene the redheaded mice withstood twice as much pressure as wild-type mice with black fur and remained in contact with a 52°C hot plate for about five seconds longer than the others. To explain this increased pain tolerance, the scientists first wondered whether melanocytes were part of the equation. According to their experiments, yes, they are one of the variables to be taken into account, since the MC1R mutation alters the molecules they produce.
In redheads, melanocytes no longer produce enough proopiomelanocortin, a precursor protein for several hormones, such as β-endorphin and Melanocyte-stimulating hormone. These no longer interact with their receptors: an opioid receptor for β-endorphin and the MC4R for Melanocyte-stimulating hormone at the level of nociceptor neurons. The opioid receptor is also stimulated by other non-proopiomelanocortin-derived hormones, but the MC4R remains inactive in redheads.
Thus, with a receptor that remains passive, nociceptor neurons require a greater pain stimulus to activate, consistent with the particularly high pain tolerance threshold observed in redheads, and also with their sensitivity to opioids.