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Hair Growth
Hair grows from a single papilla, or bud, deep
in the follicle in the skin's lower layer. The follicle is nourished by its own blood supply.
Each hair shaft consists of three concentric
layers; the outer layer, composed of overlapping, scaly cells; the middle layer, or cortex,
which gives hair its bulk and colour; and the
central core, or medulla, composed of transparent cells and air spaces. In the same way
as skin cells, hair cells move
upward from the root as they mature, so that
the visible part of the hair shaft is composed
entirely of dead scales of keratin protein - the
same substance as the skin's horny layer.
PHASES OF Growth
Everyone is born with a genetically determined quota of follicles - on average 120,000 per head, although blondes have
slightly more, redheads fewer. The size of the follicle determines hair thickness. Fine hair tends to be straight and limp,
with the exception of fine black (Afro) hair. Oriental hair is
wider in diameter than Caucasian hair.
Hair grows at a seasonal rate - faster in summer than in
winter. The growth, or anagen, phase of each individual hair
varies from person to person but is generally between three
and five years. When the growth phase ends, the hair follicle
enters a resting, or catagen, phase which lasts around three
months. In the final, or telogen, phase, a new hair forms in
the follicle, pushes out the old hair and the cycle begins
again. Hairs are lost at a rate of between 20 and 100 every
day. It's also thought that hair goes through "moult" phases:
you may notice more stray hairs in the sink or brush during
spring and autumn.
There are always new hairs on the way to replace shedding ones, although the rate of hair growth is controlled by
hormones. In women, oestrogen prevents hair growing on the
face and diverts it to the head, which is why women tend to
have more lustrous hair than men. Consequently when
oestrogen levels drop during the menopause, hair becomes noticeably thinner. The diameter of individual hairs begins to
decrease much earlier, at the age of about 25, especially in
women, accounting for the gradual loss in "body'. Sadly, some
women may begin to lose hair.
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