The Genetics of Hair Color

Natural hair color comes from the pigmentation of hair follicles due to two types of melanin, eumelanin and pheomelanin. Generally, if more melanin is present, the color of the hair is darker; if less melanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color. Natural hair color can be black, brown, blond, or red, depending on a person's ethnic origins. Hair color is typically genetically associated with certain skin tones and eye colors.

Brown hair is the most common in Europe and most of the United States and some other parts of the world. It is characterized by higher levels of eumelanin and lower levels of pheomelanin.

Black hair is the darkest hair color. It has large amounts of eumelanin and is less dense than other hair colors. It can range from soft black to blue-black or jet-black hair. It is also the shiniest of all hair colors.

Blond hair can have almost any proportion of pheomelanin and eumelanin, but both only in small amounts. More pheomelanin creates a more golden blond color, and more eumelanin creates an ash blond.

Blond hair is common in many European peoples, but rare among peoples of non-European origin.
Auburn hair ranges from light to reddish brown. The chemicals which cause auburn hair are eumelanin (brown) and pheomelanin. It is most commonly found in individuals of European descent.

Red hair ranges from vivid strawberry shades to deep auburn and burgundy. It is caused by a variation in the Mc1r gene and believed to be recessive.

Grey hair color typically occurs naturally as people age. For some people this can happen at a very young age (i.e.: at the age of 10). The same can be said for white hair. In some cases, grey hair may be caused by thyroid deficiencies or a deficiency of B12.

Changes in hair color typically occur naturally as people age, eventually turning the hair gray and then white. This is called achromotrichia. More than 40 percent of Americans have some gray hair by age 40, but white hairs can appear as early as childhood. The age at which graying begins seems almost entirely due to genetics. Sometimes people are born with gray hair because they inherit the trait.

There are several medical conditions effecting haircolor which include:

Albinism is a genetic abnormality in which little pigment is found in human hair, eyes or skin. The hair is white or pale blond.

Vitiligo is a patchy loss of hair and skin color that may occur as the result of an auto-immune disease.

Malnutrition is also known to cause hair to become lighter, thinner, and more brittle. Dark hair may turn reddish or blondish due to the decreased production of melanin. The condition is reversible with proper nutrition.

Werner syndrome and pernicious anemia can also cause premature graying.

A recent study demonstrated that people 50–70 years of age with dark eyebrows but gray hair are significantly more likely to have type II diabetes than those with both gray eyebrows and hair.

A 1996 British Medical Journal study conducted by J.G. Mosley, MD found that tobacco smoking may cause premature graying. Smokers were found to be four times more likely to begin graying prematurely, compared to nonsmokers.

Gray hair may temporarily darken after inflammatory processes, after electron-beam-induced alopecia, and after some chemotherapy regimens. Much remains to be learned about the physiology of human graying.