Red Head Beauty

 

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Red hair occurs naturally in 1–2% of the human population. It occurs more frequently (2–6%) in people of northern or western European ancestry, and less frequently in other populations. Red hair appears most commonly in people with two copies of a recessive gene on chromosome 16 which causes a mutation in the MC1R protein.

Red hair varies from a deep burgundy through burnt orange to bright copper. It is characterized by high levels of the reddish pigment pheomelanin and relatively low levels of the dark pigment eumelanin. The term redhead has been in use since at least 1510. It is associated with fair skin color, lighter eye colors (gray, blue, green, and hazel), freckles, and sensitivity to ultraviolet light.

Cultural reactions have varied from ridicule to admiration; many common stereotypes exist regarding redheads and they are often portrayed as fiery-tempered.

Pain tolerance and injury

Two studies have demonstrated that people with red hair have different sensitivity to pain compared to people with other hair colors. One study found that people with red hair are more sensitive to thermal pain (associated with naturally occurring low vitamin K levels), while another study concluded that redheads are less sensitive to pain from multiple modalities, including noxious stimuli such as electrically induced pain.

Researchers have found that people with red hair require greater amounts of anesthetic. Other research publications have concluded that women with naturally red hair require less of the painkiller pentazocine than do either women of other hair colors or men of any hair color. A study showed women with red hair had a greater analgesic response to that particular pain medication than men. A follow-up study by the same group showed that men and women with red hair had a greater analgesic response to morphine-6-glucuronide.

The unexpected relationship of hair color to pain tolerance appears to exist because redheads have a mutation in a hormone receptor that can apparently respond to at least two types of hormones: the pigmentation driving melanocyte-stimulating hormone (MSH), and the pain relieving endorphins. (Both derive from the same precursor molecule, POMC, and are structurally similar.) Specifically, redheads have a mutated melanocortin-1 receptor (MC1R) gene that produces an altered receptor for MSH. Melanocytes, the cells that produce pigment in skin and hair, use the MC1R to recognize and respond to MSH from the anterior pituitary gland. Melanocyte-stimulating hormone normally stimulates melanocytes to make black eumelanin, but if the melanocytes have a mutated receptor, they will make reddish pheomelanin instead. MC1R also occurs in the brain, where it is one of a large set of POMC-related receptors that are apparently involved not only in responding to MSH, but also in responses to endorphins and possibly other POMC-derived hormones. Though the details are not clearly understood, it appears that there is some "cross talk" between the POMC hormones that may explain the link between red hair and pain tolerance.

There is little or no evidence to support the belief that people with red hair have a higher chance than people with other hair colors to hemorrhage or suffer other bleeding complications. One study, however, reports a link between red hair and a higher rate of bruising.