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Hair Color: Red Hair

Hair color is a result of pigmentation (coloration) due to the presence of two chemical substances of melanin: eumelanin and pheomelanin. Generally, when more melanin is present, the darker the hair color; when less, it is lighter.

Natural hair colors

Natural hair color is black, brown (chestnut), blond and red. Hair color is genetically associated with skin color and eye color. Black hair is the most common while blond and red hair is associated more frequently with genetic characteristics such as albinism, and with illness such as skin cancer.

Genetics and biochemistry of hair color

Two types of pigment give hair its color: eumelanin and pheomelanin. Eumelanin is black and brown while pheomelanin is red.

Higher levels of eumelanin in the hair determine how dark it is. For example, a lower concentration of brown eumelanin will cause the hair to be blonder and a higher eumelanin concentration will make it browner (a much higher amount of black eumelanin will result in black while a lesser amount will make it gray).

All humans have pheomelanin in their hair. Pheomelanin is more chemically stable than black eumelanin, but less chemically stable than brown eumelanin, so it breaks down more slowly when oxidized. This is why bleach gives darker hair a reddish tinge during the artificial coloring process. As the pheomelanin continues to break down, the hair will gradually become orange, then yellow, and finally white.

According to one theory, at least two gene pairs control human hair color.

  • One phenotype (brown/blonde) has a dominant brown allele and a recessive blond allele.

Thus, a person with a brown allele will have brown hair; a person with no brown alleles will be blond.

This explains why two brown-haired parents can produce a blond-haired child.

  • The other gene pair is a non-red/red pair, where the non-red allele (which suppresses production of pheomelanin) is dominant and the allele for red hair is recessive.

Thus, a person with two copies of the red-haired allele will have red hair but it could be reddish brown, auburn or a brilliant orangey-red, depending on if the first pair of genes is brown or blond, respectively.

Response difference in redheads to some medicines

Redheads have different reactions to some medicines, especially to analgesics and anesthesia. Additionally, the majority of red-haired women have a small mutation in an allele (MC1R gene) which causes a greater response to some analgesics (they need less to get the same effect) than the rest of redheads or persons with other hair colors.

Some NCBI (National Center for Biotechnology Information) researchers have found that people with red hair require greater amounts of certain types of analgesics. Other NCBI reserch publications concluded that because of their genetics, red-haired women require a lesser amount of an analgesic called Pentazocine than women with other hair colors or than men with any hair color.

Another study by NCBI demonstrated that red-haired women had a greater response to those analgesics for a certain pain than red-haired men. A follow-up study by the same group showed that red-haired people in general (both men and women) were much more sensitive to a type of analgesic called Morphine-6-glucuronide (M6G) than persons with other hair colors.

Gene or region studied

  • MC1R
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