Human hair color: Wikis

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Human hair comes in a variety of different shades, which can be altered or enhanced artificially

Hair color is 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.

Particular hair colors can be associated with ethnic groups - however, due to migration and global travel, considerable variations have developed in the hair color of individuals within an ethnic group, creating a greatly increased diversity of hair color.

Contents

Genetics and biochemistry of hair color

Two types of pigment give hair its color: eumelanin and pheomelanin. Pheomelanin colors hair red. Eumelanin, which has two subtypes of black or brown, determines the darkness of the hair color. A low concentration of brown eumelanin results in blond hair, whereas a higher concentration of brown eumelanin will color the hair brown. High amounts of black eumelanin result in black hair, while low concentrations give gray hair. All humans have some 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 why bleach gives darker hair a reddish tinge during the artificial coloring process. As the pheomelanin continues to break down, the hair will gradually become orange, then yellow, and finally white.

The genetics of hair colors are not yet firmly established. According to one theory, at least two gene pairs control human hair color.

One phenotype (brown/blond) 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 explains why two brown-haired parents can produce a blond-haired child.

The other gene pair is a non-red/red pair, where the not-red allele (which suppresses production of pheomelanin) is dominant and the allele for red hair is recessive. 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 on 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 blonde/light brown), nor does it explain why hair color sometimes darkens as a person ages. Several gene pairs control the light versus dark hair color in a cumulative effect. A person's genotype for a multifactorial trait can interact with environment to produce varying phenotypes (see quantitative trait locus).

Natural hair colors

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.

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Brown hair

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. Of the two types of eumelanin (black and brown), brown-haired people have brown eumelanin; they also usually have medium-thick strands of hair. Brown-haired people are also known as brunettes/brunets.

Black hair

Black hair is the darkest and the most common color of human hair. 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.[1]

Blond hair

Blond hair ranges from nearly white (platinum blonde, tow-haired) to a dark golden blond. Strawberry blond, a mixture of blond and red hair only (thought to have originated in Celtic and Scandinavian countries) is a much rarer type containing the most amounts of phaeomelanin.

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. Many children born with blond hair develop darker hair as they age. In the United States, natural blonde hair occurs most likely near the Great Lakes area and in highlands.

Auburn hair

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

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.[2] Red hair has the highest amounts of pheomelanin and usually low levels of eumelanin, and is the rarest natural human hair color. [3][4][5]

Grey and white hair

Grey hair color typically occurs naturally as people age (see "Effects of aging on hair color", below). 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.[6]

The Journal of Investigative Dermatology published a study in 2005 that claimed white people will begin to gray in their mid-thirties and Asian people begin graying in their late thirties, but most black people can retain their original hair color until their mid-forties. [7] People with albinism have white hair due to low amounts of melanin.

Conditions affecting hair color

Effects of aging on hair color

A gray-haired man

Children born with some hair colors may find it gradually darkens as they grow. Many blond, strawberry blond, light brown, or red haired infants experience this.

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.

Two genes appear to be responsible for the process of graying, Bcl2 and Bcl-w. The change in hair color occurs when melanin ceases to be produced in the hair root and new hairs grow in without pigment. The stem cells at the base of hair follicles produce melanocytes, the cells that produce and store pigment in hair and skin. The death of the melanocyte stem cells causes the onset of graying.[8]

Other medical conditions affecting hair color

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.[9]

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.[10]

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.[11]

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.[12]

Changes in hair color after death

The hair color of mummies or buried bodies can change. 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).[13]

Hair coloring

A hairdresser colors a client's hair.

Hair color can be changed by a chemical process. Hair coloring is classed as "permanent" or "semi-permanent".

Permanent color, as the name suggests, permanently colors the hair - however because hair is constantly growing, the color will eventually grow out as new, uncolored hair grows in.

Permanent hair color gives the most flexibility because it can make hair lighter or darker as well as changing tone and color, but there are negatives. Constant (monthly or six-weekly) maintenance is essential to match new hair growing in to the rest of the hair, and remedy fading. A one-color permanent dye creates a flat, uniform color across the whole head, which can look unnatural and harsh, especially in a dark shade. To combat this, the modern trend is to use multiple colors - usually one color as a base with added highlights or lowlights in other shades.

Semi-permanent color washes out over a period of time – typically four to six weeks, so root regrowth is less noticeable. The final color of each strand is affected by its original color and porosity, so there will be subtle variations in color across the head - more natural and less harsh than a permanent dye. However, this means that gray and white hair will not dye to the same color as the rest of the head (in fact, some white hair will not absorb the color at all). A few gray and white hairs will blend in sufficiently not to be noticeable, but as they become more widespread, there will come a point where a semi-permanent alone will not be enough. The move to 100% permanent color can be delayed by using a semi-permanent as a base color, with permanent highlights.

Semi-permanent hair color cannot lighten hair. Hair can only be lightened using chemical lighteners, such as bleach. Bleaching is always permanent because it removes the natural pigment.

"Rinses" are a form of temporary hair color, usually applied to hair during a shampoo and washed out again the next time the hair is washed.

See also

Notes

  1. ^ "Hair Color:Two Hair Colors for an Infinite Pallette". http://www.hair-science.com/_int/_en/topic/topic_sousrub.aspx?tc=ROOT-HAIR-SCIENCE%5EAMAZINGLY-NATURAL%5ECOLOR-PALETTE&cur=COLOR-PALETTE. Retrieved 2010-02-27. 
  2. ^ In males, the supposedly recessive trait is often expressed in parts of the facial hair or beard. Valverde P, Healy E, Jackson I, Rees JL, Thody AJ (November 1995). "Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans". Nat. Genet. 11 (3): 328–30. doi:10.1038/ng1195-32810.1038/ng1195-328. PMID 7581459. 
  3. ^ http://www.azcentral.com/ent/pop/articles/0505redhair05.html
  4. ^ http://www.brighthub.com/science/genetics/articles/4704.aspx
  5. ^ http://www.mlive.com/entertainment/index.ssf/2009/11/michigan_twins_featured_in_boo.html
  6. ^ Juangbhanit C, Nitidanhaprabhas P, Sirimachan S, Areekul S, Tanphaichitr VS (June 1991). "Vitamin B12 deficiency: report of a childhood case". J Med Assoc Thai 74 (6): 348–54. PMID 1744541. 
  7. ^ Burford, Michelle (August 2009). "Gray Hair Myths and Facts". AOL Health. http://www.aolhealth.com/healthy-living/beauty-skin-care/gray-hair. Retrieved August 2009. 
  8. ^ Nishimura EK, Granter SR, Fisher DE. Mechanisms of hair graying: Incomplete melanocyte stem cell maintenance in the niche. 
  9. ^ Department of Dermatology, Academic Teaching Hospital Dresden-Friedrichstadt (2005 December;14). "Eyebrow color in diabetics". Acta Dermatovenerol Alp Panonica Adriat.: 157–60. PMID 16435045. 
  10. ^ Mosley JG, Gibbs AC (1996). "Premature grey hair and hair loss among smokers: a new opportunity for health education?". BMJ 313 (7072): 1616. PMID 8991008. PMC 2359122. http://bmj.bmjjournals.com/cgi/content/full/313/7072/1616. 
  11. ^ Cline DJ (April 1988). "Changes in hair color". Dermatol Clin 6 (2): 295–303. PMID 3288386. 
  12. ^ Cancer drug restores hair color BBC News
  13. ^ Interactive Dig Hierakonpolis - Archaeological Hair

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