Parents often cite having teenagers as the cause of gray hair.
This is a good theory, but scientists continue to investigate why
hair turns gray. In time, everyone’s hair turns gray. Your chance of
going gray increases 10-20% every decade after 30 years.
Initially, hair is white. It gets its natural color from a type
of pigment called melanin. The formation of melanin begins before
birth. The natural color of our hair depends upon the distribution,
type and amount of melanin in the middle layer of the hair shaft or
cortex.
Hair has only two types of pigments: dark (eumelanin) and light (phaeomelanin).
They blend together to make up the wide range of hair colors.
Melanin is made up of specialized pigment cells called
melanocytes. They position themselves at the openings on the skin’s
surface through which hair grows (follicles). Each hair grows from a
single follicle.
The process of hair growth has three phases:
- Anagen: This is the active growth stage of the hair fiber and
can last from 2- 7 years. At any given moment 80-85% of our hair
is in the anagen phase.
- Catagen: Sometimes referred to as the transitional phase,
which is when hair growth begins to “shut down” and stop activity.
It generally lasts 10- 20 days.
- Telogen: This occurs when hair growth is completely at rest
and the hair fiber falls out. At any given time, 10-15 % of our
hair is in the telogen phase, which generally lasts 100 days for
scalp hair. After the telogen phase, the hair growth process
starts over again to the anagen phase.
As the hair is being formed, melanocytes inject pigment (melanin)
into cells containing keratin. Keratin is the protein that makes up
our hair, skin, and nails. Throughout the years, melanocyctes
continue to inject pigment into the hair’s keratin, giving it a
colorful hue.
With age comes a reduction of melanin. The hair turns gray and
eventually white.
So why does our hair turn gray or white?
Dr. Desmond Tobin, professor of cell biology from the University of
Bradford in England, suggests that the hair follicle has a
“melanogentic clock” which slows down or stops melanocyte activity,
thus decreasing the pigment our hair receives. This occurs just
before the hair is preparing to fall out or shed, so the roots
always look pale.
Moreover, Dr. Tobin suggests that hair turns gray because of age
and genetics, in that genes regulate the exhaustion of the
pigmentary potential of each individual hair follicle. This occurs
at different rates in different hair follicles. For some people it
occurs rapidly, while in others it occurs slowly over several
decades.
In a February 2005 Science article (Nishimura, et al.)
Harvard scientists proposed that a failure of melanocyte stem cells
(MSC) to maintain the production of melanocytes could cause the
graying of hair. This failure of MSC maintenance may result in the
breakdown of signals that produce hair color.
There are other factors that can change the pigmentation of hair,
making it lighter or darker. Scientists have divided them by
intrinsic (internal) and extrinsic (external) factors:
Intrinsic factors:
- Genetic defects
- Hormones
- Body distribution
- Age
|
Extrinsic factors:
- Climate
- Pollutants
- Toxins
- Chemical exposure
|
Hair-raising facts:
- An average scalp has 100,000-150,000 hairs.
- Hair is so strong that each hair can withstand the strain of
100 grams (3.5 ounces). An average head of hair could hold 10-15
tons if only the scalp was strong enough!
- Human hair grows autonomously, that is each hair is on its own
individual cycle. If all our hair were on the same cycle, we would
molt!
- Hair has the highest rate of mitosis (cell division). An
average hair grows 0.3 mm a day and 1 cm per month.
|
