Recent research has shown that patients with red hair need larger doses of anesthesia, and that they are resistant to local pain injections.
Red-haired patients have a gene called melanocortin-1 receptor that is different than patient’s with brown, black, or blond hair. This “Mc1R” gene controls pain receptors in the brain.
Because of this genetic difference, redheads require up to 20% more general anesthetic to control their pain during surgery!