There are all sorts of (false) rumors and superstitions floating around about redheads: They bring bad luck. They have fiery tempers. They're more susceptible to pain sometimes and hate going to the dentist. On that last account, though, there's a decent amount of research that might explain the anecdotal evidence.
One of the earliest studies supporting that last notion, published in 2004, found that redheaded subjects required 19% higher dosages of an anesthetic (desflurane) to realize a satisfactory effect. The following year, another study found redheads to be more sensitive to thermal pain, and resistant to the effects of a different injected anesthetic (lidocaine). The apparent difference, for those natural carrot tops, involves the presence of melanocortin 1 receptor (MC1R) gene variants in the pigment-producing cells known as melanocytes. These variants stymie the hormones that would otherwise turn red hair a different shade, while also seemingly influencing secretions related to pain tolerance.
However, research doesn’t support the idea that redheads have a lower pain tolerance generally, and they are actually more sensitive to opioid analgesics. A 2021 studyfound that red-haired mice, which also possess the MC1R variants, have a higher threshold for certain types of pain induction. This followed a 2020 study that suggested the MC1R variants tied to pain sensitivity are distinct from those that affect hair color. That said, it does seem wise to offer redheads an extra novocaine boost at the dentist.
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