Human hair color

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"Black hair" redirects here. For unprocessed African hair, see Natural hair.

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.

Contents 1 Genetics and biochemistry of hair color 2 Natural hair colors 2.1 Black hair 2.2 Brown hair 2.3 Blonde hair 2.4 Red hair 2.5 Gray hair 3 Conditions affecting hair color 3.1 Effects of aging on hair color 3.2 Other medical conditions affecting hair color 3.3 Artificial factors affecting hair color 3.4 Changes in hair color after death 4 Hair coloring 5 See also 6 Footnotes 7 External links

[edit] Genetics and biochemistry of hair color

There are two types (three subtypes) of pigment that give hair its color: Eumelanin & Pheomelanin, Eumelanin is black and brown while 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 blonde, whereas more brown eumelanin will give it a brown color. 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.

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.

[edit] Natural hair colors

Natural hair color is 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 {cn}. Blond and red hair are sometimes associated with disorders such as skin cancer or albinism. ^[1]

Blackblack.jpg Black hair

Longbrown.jpg Brown hair

Blond profile.jpg Blond hair

Woman redhead natural portait.jpg Red hair

[edit] Black hair

Main article: Black hair

Black hair is the darkest and most common color of human hair. Black hair is most commonly found in people of non-European 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 a very dark brown or complete black. Black hair is known to be the shiniest out of all other hair colors.^[2]

[edit] Brown hair

Brown hair is the second most common hair color (after black hair) and is also found all over the world (mostly European, Middle Eastern, African, or some Native American heritage). It is characterized by higher levels of the dark pigment eumelanin and lower levels of the pale pigment phaeomelanin. Of the two types of eumelanin (black and brown), brown-haired people have brown eumelanin. Brown-haired people have medium-thick strands of hair. Brown haired people can range highly in skin and eye color. A brown-haired male may be called a brunet, though this usage is relatively uncommon; a brown-haired female may be called a brunette.

[edit] Blonde hair

Main article: Blonde

Blonde hair is a relatively rare human phenotype due to its association with recessive genes, occurring in approximately 2% of the world population^{[citation needed]} with the majority of natural blondes being of European descent.

Blonde hair ranges from nearly white (platinum blonde, tow-haired--though this shade is extremely rare) to a dark golden blonde. Strawberry blonde (found predominantly in the British Isles) is an especially rare type (the most pheomelanin): a mixture of blonde and red hair. Blonde hair can have almost any proportions of pheomelanin and eumelanin, but both only in small amounts. More pheomelanin creates a more golden blonde color, and more eumelanin creates an ash blonde. The most pheomelanin creates a strawberry blonde. Natural blondes have the thinnest strand of hair. Males with this hair color are blond; females are blonde.

[edit] Red hair

Main article: 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 believed to be recessive.^[3] Red hair has the highest amounts of pheomelanin and usually low levels of eumelanin.^{[citation needed]}

[edit] Gray hair

Gray hair color typically occurs naturally as people age. (See "Effects of aging on hair color", below.) In some cases, gray hair may instead be caused by a deficiency of B12 or a thyroid imbalance.^[4]

[edit] Conditions affecting hair color

[edit] 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 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.^[5]

[edit] 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.^[6]

[edit] 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.^[7]

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.^[8]

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.^[9]

[edit] 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).^[10]

[edit] Hair coloring

Main article: Hair coloring

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. Semi-Permanent hair color is only a deposit of hair color. This hair color is used to darken natural 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.

[edit] See also

• Eye color
• Human skin color
• List of Mendelian traits in humans

[edit] Footnotes

[edit] External links

• A chart of hair colors

v • d • e Human hair
By area	Head hair · Androgenic hair (Facial hair · Chest hair · Underarm hair · Abdominal hair · Pubic hair · Leg hair)	Image:Human hair closeup-08960-nevit.jpg
By type	Vellus hair · Terminal hair · Lanugo
Related topics	Human hair color · Hairstyle · Hypertrichosis · Trichophilia · Hair removal · Hair loss

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