Hair Color
Pigmentation
Color is perhaps the most obvious characteristic of hair, but as far as we know it has no biological function in humans. It does not protect the hair from the harmful effects of sunlight (although hair itself protects the scalp, of course).
As we have seen, the color of hair is due to the presence in the cortex of granules of a pigment called melanin, which is formed in special pigment-producing cells (melanocytes) in the hair bulb during the growing phase (anagen) of each hair. The melanin granules lie along the amino acid chains of the proteins, looking under the microscope rather like a string of pearls.
Melanin is found in two forms. Eumelanin is the dark pigment which predominates in black and brunette hair. Phaeomelanin is a lighter pigment, which is found in red and blond hair. Many people's hair contains a mixture of the two: the more eumelanin there is in the mixture, the darker is the hair. The mixture (and the shade) varies not only from one person to another, but also across one person's head. The combination of pigments in the mixture is determined by the individual's genes. Differences between dark-haired people are due to differences in the overall quantities of melanins in their hair.
Eumelanin granules are oval (elliptical) in shape, fairly uniform in their make-up and quite hard, with sharply defined edges. Phaeomelanin granules are smaller, partly oval and partly rod-shaped.
The range of colors produced by melanins is limited to shades of yellow, brown, red and black. Grey hairs contain only a few melanin granules, spread out through the hair. White hairs contain no melanin at all: their whiteness is an optical effect, due to the way they reflect the light. Surprisingly, however, unpigmented hairs look yellow (the 'color' of keratin) when they first grow, and only later turn white.
Genetic differences
Ethnic differences in hair color are as obvious as are differences in hair type. Most people in the world have dark hair, though in northern Europe blond hair is the most common. Curiously, however, people with blond hair and/or blue eyes are found even in North Africa and the Middle East.
Melanin distribution
Melanin granules are spread out throughout the cortex of the hair. There are more of them near the outer edge of the cortex than towards the middle. The darker the hair, the more melanin granules it contains.
Effects of weathering
The ends of the hair may look lighter than the rest, because of the normal weathering that affects everyone's hair. Heavily weathered hair, which is often brittle, tends to look lighter too.
Red hair
Red hair is relatively uncommon in Europe, except in Scotland: more than one in ten Scots are redheads. Red-haired people often have pale skin that burns easily.
In red hair, nearly all the melanin is present in the form of phaeomelanin. Coloring red hair is difficult because of this different pigmentation, and bleaching red hair to a lighter shade is especially hard.
Graying hair
Gray hair is one of the most familiar signs of aging. The age when graying starts depends on one's genetic inheritance. But in half of all Caucasoid people, half the hairs on the scalp are gray by the age of 50.
The loss of hair color is due to a gradual fall in melanin production in the hair bulb. If you look at the hairs on a graying head you find a full range of color, from the normal shade through to white along each hair, and also from one hair to another. Usually people notice their first gray hairs near their temples. Then the grayness spreads to the crown, and later to the back of the head.
Rapid graying
You have probably heard stories about people who are supposed to have 'gone white overnight' following some terrible shock or grief. Treat these tales with caution! A black hair cannot of itself suddenly turn white. Hairs grow for years with pigment inside them, and since they are 'dead' there is no process by which the melanin throughout a hair can be naturally destroyed rapidly (although it may be bleached by sunlight over many years).
Apparent rapid greying may be due to a selective shedding of pigmented hair in a person who has some gray hairs which are retained. Shedding of this kind usually takes several months, but can happen within a few days. If it does take place quickly the effects can be dramatic, since the person's grey hairs may not have been at all obvious until the darker hairs were lost.
Whether stress or shock can cause this kind of hair loss (known as alopecia areata) is unknown.
of pigmented and unpigmented (white) hairs, the so-called 'salt and pepper' look. In an acute episode of alopecia areata he lost the pigmented hairs, leaving only the unpigmented ones. He recovered spontaneously, and when his hair re-grew the 'salt and pepper' mixture returned
Premature graying
Very rarely, an individual's hair may begin to turn gray at an unexpectedly early age - before the age of 20 in Caucasoids and before 30 in Africans. In some people the cause is a medical condition. More usually it is due to the presence of a particular gene.
Albinism
Albinism is an inherited condition in which there is little or no pigment in the hair. An albino's hair is startlingly pale, either light yellow or nearly white. Albino skin is also pale, even in African people.
Where the condition is severe the eyes lack pigment too, and look pink: albino people often have poor vision.
Acquired color defects
Inflammation in the hair follicle, which can occur in shingles, damages the melanocytes and may lead to loss of hair color. So too may exposure to X-rays, though very rarely a deeper color develops. Occasionally white patches form in the beard after dental treatment.
