Hair color

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Human beings have many variations in hair color (or colour) and hair texture.

Hair color is the result of pigmentation due to the presence of the chemicals of melanin. In general, the more melanin, the darker the hair color.

In general, the color of children's and adults' hair varies from pale yellow (blonde) to deep black.<ref>Despite many myths, natural black hair does exist.</ref> The ethnic distribution of colors has historically varied by geographic area. For example, deep brown and black prevail in the Middle East, North Africa, and Mediterranean Europe, and even darker shades occur in East Asia, South Asia, as well as tropical Africa and Central America; lighter brown is more common in central Europe, yellow/blond in northern Europe, and reddish in Ireland and Britain.

However, considerable differences in hair color and texture exist between individuals of similar ethnicity, and immigration and global travel have greatly increased the diversity of hair characteristics in many countries.

Names for human hair colors include:

• brunette, brown, chocolate, cinnamon, dark, chestnut
• raven, midnight, dark, sable, ebony, jet, onyx, black
• flaxen, fair, tow-headed, blonde, sandy blonde, dirty blonde, strawberry blonde, honey, golden, platinum blonde
• auburn, chestnut, red, fiery, redhead, russet, ginger, scarlet, cinnamon
• silver, salt and pepper, white, gray, alabaster, snow, platinum

People also change their hair color to colors that do not occur naturally.

Effects of aging on hair color

Image:Old Hmong Man (Sapa Vietnam).jpg A change in hair color typically occurs naturally as people age, usually turning their hair from its natural color to gray, then to white. More than 40 percent of Americans have some gray hair by their fortieth birthday but grey hairs can appear as early as the teens and twenties for some, or even in childhood. The determination of when someone begins graying, whether it comes with aging or prematurely, seems to be almost entirely based on genetics. Sometimes people are born with gray hair because it is passed down genetically.

The change in hair color is caused by the gradual decrease of pigmentation that occurs when melanin ceases to be produced in the hair root, and new hairs grow in without pigment. Two genes appear to be responsible for the process of greying, Bcl2 and Mitf. The stem cells at the base of hair follicles are responsible for producing melanocytes, the cells that produce and store pigment in hair and skin. The death of the melanocyte stem cells causes hair to begin going grey.<ref>Template:Cite journal</ref>

There are no special diets, nutritional supplements, vitamins, nor proteins that have been proven to slow, stop, or in any way affect the graying process, although many have been marketed over the years.

Many people use hair dye to disguise the amount of gray in their 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 in the study.<ref>http://bmj.bmjjournals.com/cgi/content/full/313/7072/1616</ref>

Genetics

At least two gene pairs control the overall human hair color. One gene, which is a brown/blonde pair, has a dominant brown allele and a recessive blonde allele. If a person carries the brown allele, he will have brown hair; otherwise, he will be blonde. This also explains why two brown-haired parents can produce a blonde-haired child. The other gene pair is a not-red/red pair, where the "not-red" allele (which suppresses production of phaeomelanin) is dominant and the allele for red hair is recessive. Since the two gene pairs both govern hair color, a person with two copies of the red-haired allele will have red hair, but it will be either auburn or bright reddish orange depending upon whether the first gene pair gives a brown or blonde hair color respectively. The recessive genes for both blonde and red hair are found nearly exclusively in populations of the Caucasian race.

However, the two-gene model cannot explain the various shades of brown, blonde, or red which may occur (for example, platinum blonde versus dark blonde/light brown), or why one blonde child's hair might turn brown as he grows up while another blonde child's hair does not.

According to some research, there are several gene pairs that control the light versus dark hair color in an accumulative efect. Therefore, the more of these that are dominant, the darker the hair will be.

Medical conditions affecting hair color

Albinism is a genetic abnormality where no pigment is found in human hair or eyes, making the eyes a pale blue and the hair white.

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 brittler. Dark hair may thus turn reddish or blondish due to the decreased production of melanine. 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 gray hair.<ref>Template:Cite journal</ref>

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.<ref>http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3288386&dopt=Abstract</ref>

Archaeological hair

The colour of the hair of mummies or buried peoples can change over large time periods. Hair contains a mixture of black-brown eumelanin and red-yellow phaeomelanin. Phaeomelanin is much more stable than eumelanin, so that the phaeomelanin in the hair is better preserved over time than the eumelanin. The colour of hair changes faster under extreme conditions. It changes more slowly under dry oxidising conditions (such as in burials in sand or in ice) than under wet reducing conditions (such as burials in wood or plaster coffins).<ref>http://www.archaeology.org/interactive/hierakonpolis/field/hair.html</ref>

See also

• Eye color

Footnotes

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