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 genes 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 nervous system modulate pain more intensely. It's also possible, according to Liem, that the redhead version the MC1R gene also directly affects hormones that stimulate pain receptors in the brain.
In one study, Liem and his colleagues compared the pain tolerance of sixty naturally red-haired volunteers with sixty 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.