Reader's Digest, Hair Apparent, January 2003
Do blondes have more fun? Don't know–but redheads need more anesthesia. Red hair is the first known visible genetic trait that indicates how much anesthesia a person needs.
Twenty women, ages 18 to 40, were given a common anesthetic gas. Ten had red hair, ten had dark hair. Each received a mild electric shock: Those who twitched were given more anesthetic until reflexes stopped; those who didn't got less until the reacted.
Redheads needed 20% more gas than brunettes, said anesthesiologist Daniel Sessler of the University of Louisville. The link may occur because a genetic variation that produces red pigment also triggers higher levels of the hormone that increases pain sensitivity. Blonds should respond like brunettes because the share the same pigment, only less.