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The colour (pigmentation)
of hair is produced by melanocytes, specialised cells that
synthesise the pigment melanin. The melanocytes that synthesise
melanin for hair are located in the hair follicle. Melanocytes
are also distributed throughout the body: in the eyes, the ears,
the central nervous
system, mucous membranes and skin.
Melanocytes in the hair follicle are active only during the anagen
(growth) phase of the hair cycle. No melanin is synthesised during
the catagen (degradation) or telogen (resting) phases of the
hair cycle.
Two major types of melanin are synthesised by melanocytes. Different
melanocytes are, however, specialised to synthesise just
one type of melanin:
• Eumelanin: a brown/black pigment
that gives the colour to brown and black hair, is synthesised
by oval-shaped
melanocytes; and,
• Pheomelanin: a yellowish to reddish-brown pigment that
gives colour to red and blond hair, is synthesised by spherical melanocytes.
Melanocytes usually synthesise only one form of melanin at a
time. The melanin is taken up by structural proteins located
in the cortex at the centre of the hair shaft. The synthesis
of melanin and transfer of melanin into hair shaft proteins is
regulated by genetically programmed enzymes and other regulatory
molecules. Variations in hair colour shades can be caused by
the amount of eumelanin or pheomelanin taken up by the hair shaft
proteins, or by the presence in the hair shaft of both types
of melanin - for example, in dusky red auburn hair.
More subtle variations in hue and shade may be caused by (1)
reflection and refraction of light from internal interfaces of
structural proteins in the hair shaft, or (2) reflection or refraction
of light from hair-styling chemicals that coat the hair shaft
(the "sheen" promised by advertising for hair-styling
products). White hair contains no melanin. |
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| There are 90,000 to 150,000 hairs on the scalp,
if there has been no hair loss beyond the roughly 100 hairs that
are lost daily by normal hair cycling. Blond colour is associated
with the largest number of scalp hairs (about 140,000 to 150,000),
followed by brown (up to 140,000), black (100,000 to 120,000)
and red (90,000). |
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Hair volume can be defined as hair that maintains
body and fullness, continues holding a shape and has height and
lift away from the head.
The volume of a person's hair will be determined by the hair
diameter (i.e. the size of each hair strand), the density (how
much hair you have per square centimeter), the stiffness of the
hair, the curl in the hair (curly hair will have more density
than straight hair if taken per hair) and finally the degree
to which hairs stick together. As such, hair volume is due to
physiological factors, and is also therefore genetic in nature. |
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