Hair :: Color
Hair fiber has no color, bleach any hair and the fiber looks white simply because it reflects light. Hair color is provided by pigments produced by cells called "melanocytes". The pigments are called "melanin". Melanin actually means black so strictly speaking we should only use this word when talking about black hair. However, today scientists and dermatologists use the word melanin when talking about any kind of hair pigment blonde, red, brown, or black.
In humans, melanocyte cells are found diffusely scattered in the skin and also in little clusters in the hair follicles. Melanocytes respond to various stimulants to produce more or less melanin. Sunlight exposure makes the melanocytes in the skin produce more pigment and we get a tan (unless you are of Celtic ancestry like me). In some other mammals, such as rats and mice, melanocytes are exclusively found located in hair follicles and not in the skin between the hair follicles. Rats and mice cannot get sun tans. But I digress. The melanocytes of the skin and the melanocytes of the hair follicles are essentially the same. It is thought that the melanocytes in hair follicles can act like a storage depot for supplying the skin with melanocytes. This becomes very apparent then the skin is damaged and depleted of melanocytes. Studies show the melanocyte cells migrate from the hair follicles to repopulate the melanocyte deficient skin.
Melanocytes in hair follicles are primarily located in the hair bulb at the bottom of hair follicles. They sit in a group just above the dermal papilla along with the matrix cells that produce the hair fiber. For the melanocytes, this is the ideal location to produce pigment and have it incorporated into the growing hair fiber. There are melanocytes located in other regions of the hair follicle such as the root sheaths that surround the hair fiber. However, it is thought that these melanocytes do not significantly contribute to coloring the hair fiber.
Melanocytes produce melanin pigment proteins in their cell cytoplasm. The pigment is accumulated in membrane bound vesicles in the cell called "melanosomes". Melanocytes are usually very easy to identify in a skin biopsy because they are full of these melanosomes. In black hair producing follicles, the melanosomes in the melanocytes are very large oval shaped and gradually become densely filled with pigment proteins. People with lighter colored hair have less melanin protein in their melanosomes. Blonde haired people have melanosomes with a low density and patchy deposition of melanin. People with red and blonde hair have melanosomes that are smaller and spherical in shape and the individual melanin pigment granules inside the melanosomes are also smaller.
The matrix keratinocytes that produce the hair fiber cluster around the melanocyte cells. The melanocyte cells release their melanosomes to the keratinocytes through dendritic processes. The keratinocytes actively phagocytose the melanosomes (which means the keratinocytes "eat" the melanosomes by surrounding them and pulling them into the cell). Once the keratinocyte cells have melanosomes inside them they are then formed into the hair fiber and thus the hair fiber has color.
In humans, melanocyte cells are found diffusely scattered in the skin and also in little clusters in the hair follicles. Melanocytes respond to various stimulants to produce more or less melanin. Sunlight exposure makes the melanocytes in the skin produce more pigment and we get a tan (unless you are of Celtic ancestry like me). In some other mammals, such as rats and mice, melanocytes are exclusively found located in hair follicles and not in the skin between the hair follicles. Rats and mice cannot get sun tans. But I digress. The melanocytes of the skin and the melanocytes of the hair follicles are essentially the same. It is thought that the melanocytes in hair follicles can act like a storage depot for supplying the skin with melanocytes. This becomes very apparent then the skin is damaged and depleted of melanocytes. Studies show the melanocyte cells migrate from the hair follicles to repopulate the melanocyte deficient skin.
Melanocytes in hair follicles are primarily located in the hair bulb at the bottom of hair follicles. They sit in a group just above the dermal papilla along with the matrix cells that produce the hair fiber. For the melanocytes, this is the ideal location to produce pigment and have it incorporated into the growing hair fiber. There are melanocytes located in other regions of the hair follicle such as the root sheaths that surround the hair fiber. However, it is thought that these melanocytes do not significantly contribute to coloring the hair fiber.
Melanocytes produce melanin pigment proteins in their cell cytoplasm. The pigment is accumulated in membrane bound vesicles in the cell called "melanosomes". Melanocytes are usually very easy to identify in a skin biopsy because they are full of these melanosomes. In black hair producing follicles, the melanosomes in the melanocytes are very large oval shaped and gradually become densely filled with pigment proteins. People with lighter colored hair have less melanin protein in their melanosomes. Blonde haired people have melanosomes with a low density and patchy deposition of melanin. People with red and blonde hair have melanosomes that are smaller and spherical in shape and the individual melanin pigment granules inside the melanosomes are also smaller.
The matrix keratinocytes that produce the hair fiber cluster around the melanocyte cells. The melanocyte cells release their melanosomes to the keratinocytes through dendritic processes. The keratinocytes actively phagocytose the melanosomes (which means the keratinocytes "eat" the melanosomes by surrounding them and pulling them into the cell). Once the keratinocyte cells have melanosomes inside them they are then formed into the hair fiber and thus the hair fiber has color.
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