human hair color
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Hair color is the result of pigmentation due to the presence of the chemicals eumelanin and pheomelanin. In general, the more melanin present, the darker the hair color; the less melanin, the lighter the hair color. Black hair predominates outside of Europe. A person's hair color may also change over time and may be more than one color at a time. Considerable differences in color and texture exist between individuals of similar ethnicity, and immigration and global travel have greatly increased the diversity of hair characteristics among many countries.
Pigment
There are two types (three subtypes) of pigment that give hair its color: Eumelanin (black and brown) and pheomelanin. Eumelanin is black and brown and pheomelanin is red.
The amount of eumelanin in hair determines the darkness of its color. A low concentration of brown eumelanin in the hair will make it blond, whereas more brown eumelanin will give it a brown colour. Much higher amounts of black eumelanin will result in black hair, and a low concentration of black eumelanin in the hair 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 the reason bleach will cause darker hair to turn reddish brown during the artificial coloring process. As the pheomelanin continues to break down, the hair will gradually become orange and, later, yellow and then white.
Effects of aging on hair color
- See also: Gray hair
A change in hair color typically occurs naturally as people age, usually turning their hair from its natural color to gray and then to white. More than 40 percent of Americans have some gray hair by their fortieth birthday, but white hairs can appear as early as childhood. The age at which graying begins seems to be almost entirely based on genetics. Sometimes people are born with gray hair because it is passed down genetically. Some people use hair dye to disguise the amount of gray in their hair.
The change in hair color is caused by the gradual decrease of pigmentation that occurs when melanin ceases to produced in the hair root and new hairs grow in without pigment. Two genes appear to be responsible for the process of graying, 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 the onset of graying.[1]
Other medical conditions affecting hair color
Albinism is a genetic abnormality in which no pigment is found in human hair, eyes or skin. This results in gray, blue, or red eyes. The skin is pale and 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 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 grey hair.[2]
Artificial factors affecting hair color
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.[3]
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 greying.[4]
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. French scientists treating leukemia patients with a new cancer drug noted an unexpected side effect: some of the patients' hair color was restored to their pre-gray color.[5]
Changes in hair color after death
The hair color of mummies or buried bodies can change over large time periods. Hair contains a mixture of black-brown-yellow eumelanin and red pheomelanin. Eumelanin is less chemically stable than pheomelanin and breaks down faster when oxidized. It is for this reason that Egyptian mummies have reddish hair. The color of hair changes faster under extreme conditions. It changes more slowly under dry oxidizing conditions (such as in burials in sand or in ice) than under wet reducing conditions (such as burials in wood or plaster coffins).[6]
Genetics
light color hair
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The genetics of hair color are not yet firmly established. According to one popular theory, at least two gene pairs control human hair color. One gene, which is a brown/blond pair, has a dominant brown allele and a recessive blond allele. A person with a brown allele will have brown hair; a person with no brown alleles will be blond. This also explains why two brown-haired parents can produce a blond-haired child. The other gene pair is a not-red/red pair, where the not-red allele (which suppresses production of pheomelanin) 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 brown or blond hair, respectively.
The two-gene model does not account for all possible shades of brown, blond, or red (for example, platinum blond versus dark blond/light brown), nor does it explain why hair color sometimes darkens with age. Several gene pairs control the light versus dark hair color in a cumulative effect. Therefore, the more of these that are dominant, the darker the hair will be.
In the map to the right, "light" hair refers to blond, red, and light brown.
Common hair colors
Natural hair color is generally black, brown, blond, or red, depending on the ethnic origins of the person in question. Black hair is the most common. Hair color is genetically associated with certain skin tones and eye colors. Blond and red hair are sometimes associated with disorders such as skin cancer or albinism. [7]
Black hair
Black hair is most commonly found in people of African or Asian heritage, but occurs in people of all backgrounds and ethnicities. It has large amounts of eumelanin and is less dense than other hair colors. It can be almost completely black or very deep black with different hair texture depending on the person.
Brown hair
Brown hair is also found all over the world (mostly European heritage). Brown hair has more eumelanin than blond hair but also has much less than black. Brown-haired people have medium-thick strands of hair. A brown-haired male is a brunet; a female is a brunette.
Blond hair
Blond hair is a relatively rare human phenotype due to its association with recessive genes, occurring in approximately 2% of the world population with the majority of natural blonds being white. Blond hair ranges from nearly white (platinum blond, tow-haired) to a dark golden blond. Strawberry blond (found predominantly in the British Isles) is an especially rare type (the most pheomelanin): a mixture of blond and red hair. Blond hair can have almost any proportions of pheomelanin and eumelanin, but both only in small amounts. More pheomelanin creates a more golden blond color, and more eumelanin creates a "dishwater" or ash blond. The most pheomelanin creates a strawberry blond. Natural blonds have the thinnest strand of hair. Males with this hair color are blond; females are blonde.
Red hair
Red hair is the least common hair color. It ranges from vivid strawberry shades to deep auburn and burgundy. Celtic heritage is common with red hair.
Red hair is caused by a mutation of the Mc1r gene and is believed to be recessive.[8] Red hair has the highest amounts of pheomelanin and usually low levels of eumelanin. Natural redheads have the thickest strands of hair.
Hair color names
Names for human hair colors include:
- black: black, black ink, dark, domino, ebony, jet black, midnight, onyx, raven, raveonette, sable
- brown: brown, brunet/brunette, chestnut, chocolate, cinnamon, dark, mahogany
- blond: blond/blonde, dirty blond, dishwater blond, flaxen, fair, golden, honey, platinum blond, sandy blond, champagne blond, strawberry blonde, yellow, tow-headed
- red: strawberry blonde, auburn, chestnut, cinnamon, fiery, ginger, red, russet, scarlet, titian
- gray/white: alabaster, Arctic blond, grey, platinum, salt and pepper, silver, snow, white
Changing hair color with chemicals
The process of changing a person’s hair color can be done by a chemical process known as Hair Coloring. Hair Coloring can be permanent or temporary and the lasting effects are determined, in part, by the texture of the individual's hair. The use of chemical lighteners, such as “Bleach”, is one way hair is lightened or “highlighted.” This type of Hair Coloring is always permanent because it involves the removal of natural pigment, which never returns. Semi-Permanent Hair Color can darken or change the tonal value of the hair, but cannot lighten the hair and can usually be completely washed away after several shampoos. Demi-Permanent hair color is a deposit only hair color. This hair color is used to darken hair color. “Rinses” are a form of temporary hair color that are usually applied to hair during a shampoo. Their effects usually only last until the hair is shampooed or rinsed. Permanent hair color is probably the most-utilized because of its ability to affect the hair in level (lightness or darkness) as well as tone, but it comes with a unique set of potential problems, such as the need to frequently re-apply, unwanted fading and hot roots.
See also
Footnotes
- ^ Nishimura EK, Granter SR, Fisher DE (2005). "Mechanisms of hair graying: Incomplete melanocyte stem cell maintenance in the niche". Science 307 (5710): 720-4. PMID 15618488.
- ^ Department of Dermatology, Academic Teaching Hospital Dresden-Friedrichstadt. "Eyebrow colour in diabetics". Acta Dermatovenerol Alp Panonica Adriat.. PMID 16435045.
- ^ http://bmj.bmjjournals.com/cgi/content/full/313/7072/1616
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3288386&dopt=Abstract
- ^ Cancer drug restores hair colour BBC News
- ^ http://www.archaeology.org/interactive/hierakonpolis/field/hair.html
- ^ http://cogweb.ucla.edu/ep/Frost_06.html
- ^ Valverde P, Healy E, Jackson I, Rees JL, Thody AJ. Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans. Nature Genetics . 1995 Nov;11(3):328-30.
External links
| Common hair colors |
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| Black · Brown · Blond · Red |
| See also: Hair coloring · Category:Hair color |
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