Human hair color

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 are associated with ethnic groups. The shades of human hair color are assessed by Fischer–Saller scale. The Fischer–Saller scale, named after Eugen Fischer and Karl Saller, is used in physical anthropology and medicine to determine the shades of hair color. The scale uses the following designations: A (light blond), B to E (blond), F to L (blond), M to O (dark blond), P to T (brown), U to Y (dark brown/black) and Roman numerals I to IV (red) and V to VI (red blond). See also Martin–Schultz scale.

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.

Brown hair
Brown hair 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 often known as brunettes/brunets.

Black hair
Black-like hair is the darkest and most common hair color. 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.

Blond hair


Blond hair ranges from nearly white (platinum blond, tow-haired) to a dark golden blond. Strawberry blond, a mixture of blond and red hair is a much rarer type containing the most amounts of pheomelanin.

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. Many children born with blond hair develop darker hair as they age, with the majority of natural blonds developing their hair color into a very dark, almost brown, color by the time they reach middle age. Blond hair is most commonly found in Northern and Eastern Europeans and their descendants, but can be found spread around most of Europe. Blond hair is exceptionally rare among those without European heritage, however the Melanesians of New Guinea are one of the few non-European races and the only black race known to have a high blonde hair rate. This is because the Papuans/Melanesians have the highest rate of the newly-evolved ASPM haplogroup D, at 59.4% occurrence of the approximately 6,000-year-old allele. Sub-saharan African has the lowest while the caucasian race has the second highest of 50% which may also account for their wide range of hair colors..

Auburn hair
Auburn hair ranges along a spectrum of light to dark red-brown shades. The chemicals which cause auburn hair are eumelanin (brown) and pheomelanin (red), with a higher proportion of red-causing pheomelanin than what is found in average brown hair. It is most commonly found in individuals of Northern and Western European descent.

Chestnut Hair
Chestnut hair is a hair color which is a reddish shade of brown hair. In contrast to auburn hair, the reddish shade of chestnut is darker. Chestnut hair is common among the native peoples of Northern, Central, Western, and Eastern Europe.

Red hair
Red hair ranges from light strawberry blonde shades to titian, vivid oranges, copper, and less commonly "true" red. It is caused by a variation in the Mc1r gene and is recessive. Red hair has the highest amounts of pheomelanin, around 67%, and usually low levels of eumelanin. At 1-2% of the population, it is the least common hair color in the world. It is most prominently found in Scotland and Ireland. Scotland has the highest proportion of redheads; 13 percent of the population has red hair and approximately 40 percent carries the recessive redhead gene.

Grey and white hair
Grey or white hair &mdash; sometimes colloquially called "salt and pepper" &mdash; is not actually a true grey or white pigment. In fact, it is clear due to lack of pigmentation and melanin. The clear hairs appear as grey or white because of the way light reflects from the hairs. 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 (for example, at the age of 10). The same is true for white hair. In some cases, grey hair may be caused by thyroid deficiencies, Waardenburg syndrome or a deficiency of B12.

The Journal of Investigative Dermatology published a study in 2005 which found that Caucasian people will begin to grey in their mid-30s while Asian people begin greying in their late thirties, but most African-American people can retain their original hair color until their mid-forties. People with albinism may have white hair due to low amounts of melanin.

Aging
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. This is caused by genes being turned off and on during early childhood and puberty.

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 hair 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. It remains unclear why the stem cells of one hair follicle may die well over a decade before those in adjacent follicles less than a millimeter apart.

The anti-cancer drug Imatinib has recently been shown to reverse the graying process. However, it is much too expensive with potentially severe and deadly side effects to be used to alter a person's hair color. Nevertheless, if the mechanism of action of Imatinib on melanocyte stem cells can be discovered, it is possible that a safer and less expensive substitute drug might someday be developed.

Sex
Generally, black hair is more common in men than in women. A recent study found that blond and red hair are more common in women than in men.

Medical conditions
Albinism is a genetic abnormality in which little or no pigment is found in human hair, eyes or skin. The hair is often white or pale blond. However, it can be red, darker blond, light brown, or rarely, even dark brown.

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.

Artificial factors
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.

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.

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. However, 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.

Changes 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).

Hair coloring


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.