Hair color
From Wikipedia, the free encyclopedia
Hair color is the result of pigmentation due to the presence of the chemicals of melanin and phaeomelanin.
Human beings have many variations in hair color and hair texture. In general, the more melanin, the darker the hair color; the more phaeomelanin, the lighter it is. Usually the color of children's and adults' hair varies from pale yellow (blonde) to deep black. Hair may also come in more than one shade of color on one's head. As an example, the shade of one's hair color may change from a light shade to a darker one as time elapses.
The ethnic distribution of colors has historically varied by geographic area. For example, black hair prevails in the Middle East, North Africa, and Southern Europe. Dark shades also occur in East Asia, South Asia, Sub-saharan Africa and The Americas. Brown, blonde, red and black hair occurs in white Europeans and their descendents.
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. People also dye their hair to colors that do not occur naturally.
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[edit] Chemistry
There are 3 hair pigment chemicals, which are black eumelanin, brown eumelanin, and pheomelanin. As can be inferred, black eumelanin is black and brown eumelanin is brown. Pheomelanin is red. A small amount of black eumelanin in the absence of other pigments causes grey color. A small amount of brown eumelanin in the absence of other pigments causes yellow (blond) color.
[edit] 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 grey, then to white. More than 40 percent of Americans have some grey 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 greying, whether it comes with aging or prematurely, seems to be almost entirely based on genetics. Sometimes people are born with grey hair because it is passed down genetically. Many people use hair dye to disguise the amount of grey in their hair.
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>Nishimura EK, Granter SR, Fisher DE (2005). "Mechanisms of hair greying: Incomplete melanocyte stem cell maintenance in the niche". Science 307 (5710): 720-4. PMID 15618488.</ref>
There are no special diets, nutritional supplements, vitamins, nor proteins that have been proven to slow, stop, or in any way affect the greying process, although many have been marketed over the years. This may change in the near future however. French scientists treating leukemia patients with a new cancer drug noted an unexpected side effect: some of the patients' pre-grey hair color had been restored. [1]
A 1996 British Medical Journal study conducted by J.G. Mosley, MD found that tobacco smoking may cause premature greying. Smokers were found to be four times more likely to begin greying prematurely, compared to nonsmokers in the study.<ref>http://bmj.bmjjournals.com/cgi/content/full/313/7072/1616</ref>
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>
[edit] Medical conditions affecting hair colour
Albinism is a genetic abnormality where no pigment is found in human hair, eyes or skin, making the eyes blue, the hair pale white or blonde, and the skin pale white.
Vitiligo is a patchy loss of hair and skin colour 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 greying.
A recent study demonstrated that people 50-70 years of age with dark eyebrows but grey hair are significantly more likely to have type II diabetes than those with both grey eyebrows and grey hair.<ref>Department of Dermatology, Academic Teaching Hospital Dresden-Friedrichstadt. "Eyebrow colour in diabetics". Acta Dermatovenerol Alp Panonica Adriat.. PMID 16435045.</ref>
Grey 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 greying.<ref>http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3288386&dopt=Abstract</ref>
[edit] Genetics
At least two gene pairs control 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, they will have brown hair; otherwise, they 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 brown/blonde and red hair are found nearly exclusively in populations of white people. There is also a black gene, usually related to darker skinned humans.
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.
[edit] Common hair colors
Natural hair color is generally blond, 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).
[edit] Black hair
Black hair is found in peoples of East Asian, African, South Asian, Native American, Middle Eastern, Mediterranean and Pacific Islander heritage most commonly, but occurs in people of all backgrounds and ethnicities. It has large amounts of eumelanin and is 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 of East Asian descent have very straight black hair, while Africans tend to have very curly hair.
[edit] Brown hair
Brown hair is found all over the world, and is sometimes seen in those of Mediterranean, and Middle Eastern descent. Even in Scandinavia it is the most promenent hair color. Brown and blonde hair are based on the same gene. It is less common than black hair, by far. Many women with brown hair are called brunettes.
Brown hair can be found combined with any eye color or skin tone, but can also be associated with lighter eye color, pale skin, and freckles. It is most common amongst white people. It has more eumelanin than blond hair but also has phaeomelanin present, unlike the black gene. Brown-haired people have medium-thick strands of hair, with an average of 100,000 strands.
[edit] 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 being white.
Blond hair is genetically associated with lighter eye color such as blue, green, or light brown and with pale, often freckled, skin tones. It ranges from nearly white (platinum blond, tow-haired) to a dark golden blonde. Strawberry blond is a rare type: a mixture of blond and red hair. Blondness is a recessive gene. Blond hair 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, with an average of 140,000 hairs.
[edit] Red hair
Red hair is the least common hair color in the United States and in the world; around two percent of the U.S. population has red hair. It ranges from vivid strawberry shades to deep auburn and burgundy, and is found mainly in white people.
Red hair is caused by a mutation of the Mc1r gene and is believed to be recessive. It is genetically associated with lighter eye color, and pale skin tone. Red hair has the highest amounts of phaeomelanin and the lowest of eumelanin. Natural redheads have the thickest strands of hair and the lowest number of strands at 90,000.
[edit] Hair color names
Names for human hair colors include:
- brown, brunette, mahogany, chocolate, cinnamon, dark, chestnut
- jet black, raven, midnight, dark, sable, ebony, onyx, black, domino
- Flaxen, fair, tow-headed, blonde, sandy blonde, dirty blonde, strawberry blonde, honey, golden, platinum blonde
- auburn, chestnut, red, fiery, redhead, titian, russet, ginger, scarlet, cinnamon
- silver, salt and pepper, white, grey, alabaster, snow, platinum and Arctic blond
[edit] See also
[edit] Footnotes
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[edit] External links
gd:Dath na gruaige nl:Haarkleur pl:Kolor włosów ru:Пигментация волос
