The portion of the hair that we can see is called the shaft. Each
shaft of hair protrudes from its follicle, which is a tube-like
pouch just below the surface of the skin. The hair is attached to
the base of the follicle by the hair root, which is where the hair
actually grows and where it is nourished by blood capillaries. Like
the rest of the body, hairs are made of cells. As new cells form at
its root, the hair is gradually pushed further and further out of
the follicle. The cells at the base of each hair are close to the
blood capillaries, and are living.
As they get pushed further away from the base of the follicle they
no longer have any nourishment, and so they die. As they die, they
are transformed into a hard protein called keratin. So, each hair we
see above the skin is dead protein. It is the follicle, which lies
deep in the skin, that is essential in growing hair. Also, the
thickness of each hair depends on the size of the follicle from
which it is growing.
Hair growth is not a continuous process: it has several stages.
|ANAGEN PHASE. The
first phase is the growing stage. Hair grows at about 1 cm each
month, and this phase lasts for anything between 2 and 5 years.
|CATAGEN PHASE. As
this phase begins the bulb detaches from the blood supply and
the hair shaft is pushed up.
|THE TELOGEN PHASE.
This is followed by a resting stage, during which there is no
growth. This phase lasts about 5 months.
|At the end of the
resting phase, the hair is shed, and the follicle starts to grow
a new one.
|At any moment,
about 90% of the hair follicles of the scalp are growing hairs
in the first phase; only about 10% are in the resting phase.
|If a follicle is
destroyed for any reason, no new hair will grow from it.|
How baldness occurs
If any of the stages of hair growth are disrupted, the individual
may become bald. For example, if follicles shut down (meaning that
they stay in the resting phase, and then shed the hair) instead of
growing new hairs, there will be less hair on the head. Another
reason might be interference with the formation of new hair cells
at the root during the growing phase. If follicles have been
destroyed (ie., a burn, loss of layered skin or trauma), there
will be baldness in that area. An individual can also look bald if
the hairs are growing but are so fragile that they break just as
they emerge from the follicle.
Recently, scientists at Columbia University in New York announced
the discovery of a gene that appears to be the 'master switch' for
hair growth. They found the gene after comparing the genes of
hairless mice belonging to a mutant breed, and comparing the genes
of 11 members of a family who had lost all their hair. This
discovery is a step towards understanding how the hair follicle
works and how baldness happens, and may lead to effective
treatments becoming available in the future.
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