Healthy
scalp hair grows at an average daily rate
of approximately 0.35mm(1/72 inch), 1 cm
or <½ inch a month that is, about
2.5cm(1 inch) every 21/2 months. Hair grows
fastest in the summer, slowest in the winter,
speeds up under heat and friction, but slows
down when exposed to cold. Hair grows the
best between the ages of 15 to 30.
Pubic and axillary (armpit)
hair is particularly androgen-sensitive
and grows at lower androgen levels than
hair on the chest or legs. In boys, most
pubic hair is grown by age 15, followed
by the development of armpit hair two to
three years later. In girls, too, an increase
in androgens at puberty triggers growth
of pubic and armpit hair. Scalp hair, not
directly androgen-responsive, is influenced
by local amounts of a testosterone derivative,
5-Di Hydro Testosterone (5 DHT).
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