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Human beings have many variations in hair color 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.Despite many myths, natural black hair does exist. 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 Southern Europe, and even darker shades occur in East Asia, South Asia, as well as tropical (Sub-saharan) Africa and The Americas; lighter brown is more common in western, central & eastern Europe, yellow/blond in northern Europe, and reddish in the British Isles.
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:
- jet black, brunette, brown, mahogany, chocolate, cinnamon, dark, chestnut
- raven, midnight, dark, sable, ebony, jet, onyx, black, domino
- 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
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; a famous example of a human whose hair color went almost completely gray while still young is Taylor Hicks. 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.
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. This may change in the near future as French scientists treating cancer patients for a new drug found that some of the patients' hair color from before they turned grey had been restored. http://news.bbc.co.uk/1/hi/health/2180244.stm
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.http://bmj.bmjjournals.com/cgi/content/full/313/7072/1616
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 Whites and Caucasians
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 effect. 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, eyes or skin, making the eyes pale blue, the hair pale blonde & the skin pale pink (Like the skin-tone that white people usually have).
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 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 gray hair.
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.http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3288386&dopt=Abstract
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).http://www.archaeology.org/interactive/hierakonpolis/field/hair.html
Common hair colors
Hair color is generally yellow/gold, red, brown, or black depending on the ethnic origins of the person in question. Hair color is genetically associated with certain skin tones, eye colors, and even disorders (such as skin cancer or albinism in persons with blond or red hair).
Black hair
Black hair is most common in the world and it is found in peoples of Asian, African, South Asian, Native American, Middle Eastern, Mediterranean, Balkan and Pacific Islander heritage. Nearly all people of East Asian and African and most people from Middle Eastern descent have it. It is very similar to brown hair in strand thickness, abundance and genetic associations, but is completely black or very deep black with different hair texture depending on the person and the ethnicity. For example most people from Asian descent have very straight black hair.
Blond hair
Blond hair is a relatively rare human phenotype, occurring in 1.7 to 2% of the world population with the majority of natural blondes in Scandinavia and other parts of Europe, most notably on the northern part of the continent. Blond hair ranges from nearly white (platinum blond, tow-haired) to a dark golden brown. A common stereotype holds that Western men are known to prefer fair-haired women to their darker-haired contemporaries and this has caused many women to dye or bleach their hair blond.
Blond hair occurs in peoples of Europe (especially of non-Latin or Mediterranean heritage), in some areas of South Asia, and even in the Middle East. It is genetically associated with lighter eye color such as blue, green, or light brown and with pale, often freckled, skin tones. 5% of Americans are naturally blond.
Blond hair is also associated with skin cancer (as melanoma) and albinism.
Blondness is a recessive gene and a popular hoax says that the gene will be dead in 200 years.http://www.snopes.com/science/stats/blondes.asp It has more phaeomelanin than eumelanin but has less than red hair. Natural blondes have the thinnest strand of hair but have more hair on their heads than others. They have an average of 140,000 hairs.
Red hair
Of those previously mentioned, by far the least common hair color present in the United States is Red hair, shared by only around three percent of the American population. Red hair which ranges from vivid strawberry shades to deep auburn and burgundy is found in Europeans, especially in the British Isles and is associated with the Celtic nations mainly Ireland, Scotland and Wales. It is less commonly found in peoples of Japan and some other areas of the world. It is a recessive gene and believed to be an uncommon one. It is also found in the Middle East, and appears uncommonly in those of African descent.
Red hair is genetically associated with lighter eye color, especially green, blue, and light to medium brown and pale, often melanin-less skin. Red hair has the highest amounts of phaeomelanin and the lowest of eumelanin. They have the thickest strands of hair and the lowest amounts of strands at 90,000.
Brown hair
The majority of people of European origin have brown hair of varying shades. It is found all over the world, in and out of Europe, and is especially common in those of Mediterranean, Balkan, Pacific Islander, and Middle Eastern descent. Europeans also have high percentages of it. Many women with brown hair are called brunettes, especially if they are of European descent.
Brown hair is genetically associated with olive and darker tones of skin and brown eyes, however many White people often have brown hair and light eye colour and/or lighter skin tone. They have medium-thick strands of hair and about 100,000 strands of hair.
See also
Footnotes
External links
"Hair color"