[Larry_OHF]

Sorry I left out the link. here it is

The theory hinges on melanin, a pigment responsible for skin and hair color. The sun triggers a hormone that in turn triggers the production of melanin to form a tan. Redheads seldom tan easily because they have a defective receptor for that hormone -- a quirk with this "melanocortin-1 receptor" that also leaves their hair red. Without its intended receptor to dock in, the melanin-producing hormone may cross-react with a related receptor on brain cells that influences pain sensitivity, Sessler explained. That's still a theory. Here's what Sessler can say for certain: He and colleagues gave 10 healthy women with naturally red hair and 10 with dark hair the common inhaled anesthetic desflurane. Then they administered electric shocks -- not enough to do damage but enough to cause pain -- and inched the desflurane dose up or down according to the pain response until each patient was judged to be at the optimum anesthetic dose. The redheads required a 20 percent higher dose. Sessler said his lab first tested a few blondes and found they reacted the same as brunettes. That was expected since only redheads have the melanocortin-1 defect. The study doesn't address if men would react similarly -- there are gender differences for many drugs -- or if redheads would be similarly affected by non-inhaled types of anesthesia.