Do redheads really need more anesthesia?

You may have heard that, from the dental chair to the labor-and-delivery room, things hurt worse for redheads.

But do redheads really experience pain differently than other people?

Anecdotal reports from anesthesiologists and various animal and human studies suggest that having red hair is associated with an altered sensitivity to both pain itself and to pain-relieving medications, according to a 2023 review in the journal Anesthesiology and Perioperative Science. 

However, the details of how redheads' pain experience differs remain somewhat fuzzy, partially because past studies have all investigated different forms of pain, review co-author Jaideep Pandit, a consultant anesthesiologist at the Oxford University Hospitals' NHS Foundation Trust, told Live Science.

Related: How did doctors perform surgery before modern anesthesia?

Studies suggest that redheads are more sensitive to certain types of pain, but not others, Pandit said. One study found redheaded women were more sensitive to temperature-related pain and that the nerve blocker lidocaine was less effective in managing their pain than that of dark-haired women. Another study found that redheads were less sensitive to pain from electric shocks than other people.

Similarly, the link between ginger locks and pain management isn't straightforward. There's data suggesting that redheads need 20% more general anesthesia to stay sedated, and that they also require more local anesthesia to fend off pain. But data shows they're actually more sensitive to opioids, including mu-opioids, such as morphine and fentanyl, and kappa-opioids, although the latter effect may be specific to female patients.

Complicating matters, a 2015 study found no difference between redheads' and other people's responses to anesthesia or pain meds, so the data is somewhat mixed. 

While redheads may perceive some pain as more intense, they also have a higher pain threshold, according to Dr. David Fisher, chief of the dermatology department at Massachusetts General Hospital, who published a 2021 study on pain in red-haired mice. Red-haired mice and people appear to be somewhat numb to pain, at first. They don't perceive the pain until it reaches a higher threshold, but then, redheads feel it more intensely than others, Fisher said.

The pain experience of people with fiery locks has been challenging to explain, in part because humans are so genetically complex that it's tough to pinpoint a single genetic cause for their experience, Fisher told Live Science. 

So Fisher and his lab studied pain in mice, in which they had complete genetic control. With some exceptions, red hair is produced by mutations in the melanocortin-1 receptor (MC1R) gene; this gene helps control the type and amount of pigment in the hair, skin and eyes. Fisher's team studied mice that were genetically identical except for carrying a variant either for red hair or for black hair. 

To avoid bias, the researchers crossed these mice with an albino strain, so that they carried the red- or black-hair genes but didn't actually produce any pigment. "We saw exactly a difference in pain threshold between red and black hair, even when they weren't making pigment at all," Fisher said.

Why that's the case is complicated. The MC1R gene affects a protein in melanocytes, the body's pigment-making cells. Fisher's team found that, in addition to changing that protein, the redhead MC1R variant also causes mouse melanocytes — and, theoretically, human ones — to produce less of a substance called POMC.

POMC gets cut into several hormones that affect sensitivity to pain and opioids by helping control the activity of specific receptors. When mice have less POMC, it raises their pain thresholds, heightens their pain sensitivity, and reduces their responsiveness to some non-opioid pain drugs while boosting opioids' effects, Pandit said.

Red hair is believed to have offered an advantage in northern latitudes because it boosts ultraviolet absorption — a critical step in vitamin D synthesis —  but it's unclear whether redheads' altered pain and opioid sensitivity also offered advantages, Fisher said.

Although it's unknown why it evolved, the link between red hair and pain is confirmed, "which itself is fascinating," Pandit said. It's possible that doctors could eventually predict how a patient will respond to pain and pain medicines by looking at their genes.

This article is for informational purposes only and is not meant to offer medical advice.