Redheads may be hotheads, but they get colder faster. They also bruise more easily. And they feel more pain.

All this comes from a series of studies done in the last few years on people with for red hair. A true redhead produces an abundance of a yellow-red pigment called pheomelanin. (Brunettes produce the more common eumelanin, a dark brown pigment.) A redhead's prodigious pheomelanin output is the result of mutations, or variants, of the MC1R.3 gene. Redheads have two copies of this variant allele, one from each parent.

So what does this "redhead gene" have to do with sensitivity? The same gene is involved in the body's perception of pain. Edwin Liem, an anesthesiologist at the University of Louisville, suspects that when both copies of the MC1R.3 gene are variants, as they are in redheads, receptors in the modulate pain more intensely. It's also possible, according to Liem, that the redhead version of the MC1R gene also directly affects that stimulate pain receptors in the brain.

In one study, Liem and his colleagues compared the pain tolerance of 60 naturally red-haired volunteers with 60 brunettes. The redheads reported that they felt a chilling pain at around 6 degrees C (43 degrees F), unlike the volunteers with dark hair. Brunettes did not feel an aching chill until the temperature approached freezing.

In another experiment, also led by Liem, women with various hair color types were exposed to electric shock. Turns out, the redheads needed about 20 percent more anesthetic to relieve the pain (confirming the common belief among anesthesiologists that redheads are tough to knock out). While redheads have normal blood counts and coagulate blood the same as anyone else, they bruise more easily. Yet another study found that redheads are more than twice as likely as women with other hair colors to and avoid the dentist.

These studies have been done on women only, and it's unknown whether red-haired men would have the same outcome. (However, there's evidence that pain pathways differ between the sexes.)

Redheads are stereotyped as being hot-headed, tempestuous, dramatic, high-strung. Is it possible that a genetic sensitivity to pain can affect temperament? It's fun to speculate. For some, physical pain may translate into emotional pain. Sensitivity may tip over into volatility. Could a fiery, short temper even be a pain avoidance mechanism? Why not? After all, a good offense can be the best defense.