The Growth of a Hair
Each hair follicle is genetically programmed
before birth to either become sensitive to the
male hormones that begin to appear during puberty
– causing the follicle to eventually shrink
and die – or to not become sensitive and
continue growing throughout life.
Every single hair on
the scalp grows for two to six years, remains
for a time, and then falls out. In fact, every
day one loses 50 to 150 hairs. When a hair falls
out, a new hair begins growing in its place.
Sometimes, testosterone affects this normal growth
cycle. Hair follicles, the tiny cup-shaped structures
from which hairs grow, start to shrink. In men,
this only happens on the front and top of the
scalp since the back and sides are programmed
to grow for life. In women, hair loss is spread
out over the scalp while retaining the natural
hairline in many cases.
As the follicles shrink, the resulting hair
is thin and sparse. Eventually the follicles
shrink to the extent that new hair cannot grow.
The result is male or female pattern baldness.