Hair grows everywhere on the human skin except on the palms of our hands and the soles of our feet, but many hairs are so fine they're virtually invisible. Hair is made up of a protein called keratin that is produced in hair follicles in the outer layer of skin. As follicles produce new hair cells, old cells are being pushed out through the surface of the skin at the rate of about six inches a year. The hair you can see is actually a string of dead keratin cells. The average adult head has about...
Like the cure for cancer, those new treatments aren't nearly
ready for prime time. But they're coming, promises George Cotsarelis, MD,
director of the Hair and Scalp Clinic at the University of Pennsylvania,
"In the last 5 to 7 years there has been a boom in the
understanding of hair loss," Cotsarelis tells WebMD. "We've made great
strides at the level of basic research. Now the question is how we can convert
these findings into clinical benefits. Those kinds of leaps really take
The great leap would be to grow new hair on bald heads. But
smaller steps aren't that far away.
Why do we care about a cure for baldness? Look around you. Hair
loss is extremely common, it usually happens when the normal process of hair
growth gets disrupted.
What We Know About Hair
"The hair is real. It's the head that's a
Until it's gone, hair is easy to take for granted. But a close
look reveals the hair follicle to be one of the most interesting organs of the
body. It's most unusual feature: It is self-regenerating.
Hair follicles live just below the top layer of the skin. You
have them all over your body except, fortunately, on your lips, palms, and
At the base of the follicle is the hair bulb, where wildly
growing matrix cells become hair.
A little farther up the follicle is the mysterious feature
called the bulge. That's where follicle stem cells live. When they get the
right set of chemical signals, these self-renewing cells divide. They don't
divide like normal cells, in which both halves become new cells that keep
splitting and developing. Only one half of the follicle stem cell does that.
The other half becomes a new stem cell, and stays put for future
Hair growth goes through several distinct stages:
Anagen. The growth phase of hair. An unknown signal tells follicle
stem cells to do their thing. Next, the permanent part of the follicle -- the
dermal papilla -- gives the "go" signal to hair matrix cells. Those
cells grow wildly and become pigmented, creating a new hair shaft. At any given
time, 90% of hair cells are in this stage.
Exogen. The new hair shaft pushes the old, dead hair shaft out of
the skin. The old hair falls out.
Anagen finished. The new hair extends beyond the surface of the skin
and keeps growing. The hair shaft fully matures.
Catagen. The lower two-thirds of the follicle shrivels up and is
destroyed. The dermal papilla remains attached to the regressing follicle.
Telogen. The withered follicle rests. It waits for a signal telling
it to start all over again.
Losing hair is part of a normal cycle of growth and
replacement. Hair follicles go through the growth and resting cycle in a
nonsynchronized fashion. But sometimes things go wrong.