At less than 2% of the human population, red-haired people are rare. And it’s not only the color of their hair that makes them unique; their melanocytes, or pigment-producing skin cells, have an inactive variant of a hormone receptor called melanocortin 1. Typically, when this receptor is activated by hormones, melanocytes switch from producing yellow and red pigments to brown and black pigments. The inactive variant of this receptor in redheads is why their skin doesn’t tan. As it turns out, the receptor may also be connected to another unique trait that some studies have found red-haired people to have—a higher threshold for pain.
To study these connections, scientists looked at red-haired mice that also have higher pain thresholds and a non-functioning version of this receptor. They found that the inactive receptor caused the mice’s melanocytes to secrete lower levels of a molecule called POMC. POMC produces hormones, one of which causes increased sensitivity to pain, and another one of which blocks pain.
Since the mice have lower levels of both hormones, you’d think any effects would cancel each other out. However, bodies have additional ways of activating pain-blocking receptors. Lower levels of the hormones that cause increased sensitivity to pain, plus the body working to block pain in other ways, results in a net effect of a higher pain threshold.
Scientists think that what they’ve observed in these red-haired mice might happen in the bodies of red-haired people as well. If that’s true, you can thank your rare red-haired friends for helping scientists figure out the best ways to treat pain in everyone.
