Here's why your hair turns gray as you age
Most of us find our first
"grays" by the time we turn 30, usually at the temples, then later,
across the scalp. While many people find the salt and pepper look appealing,
others go to great lengths to conceal these locks.
The gray hair "rule of
thumb" is that by the age of 50, half of the population have lost the
color in 50% of their hair. When researchers tested this rule, they found that 74% of people aged between 45 and 65
had gray hair, with an average intensity of 27%.
Generally, men have more gray hair
than women. Asians and Africans have less gray hair than Caucasians.
What
determines the color of hair?
Hair color is produced by cells
known as melanocytes, which migrate into the hair bulb as the hair follicles
develop in utero. The melanocytes produce pigment that is incorporated into the
growing hair fibers to produce hair in a bewildering array of natural shades.
Hair color depends on the presence
and ratios of two groups of melanins: eumelanins (brown and black pigments) and
pheomelanins (red and yellow pigments). While variations in the ratio of these
pigments can produce a large number of colors and tones, siblings often have
strikingly similar hair color.
Hair color varies according to body
site, with eyelashes being darkest because they contain high levels of
eumalanin. Scalp hair is usually lighter than pubic hair, which often has a red
tinge, because of the presence of more phaeomelanin pigments. A red tinge is
also common in underarm and beard hair, even in people with essentially brown
hair on their scalp.
Hormones such as melanocyte-stimulating hormone can darken light
hair, as can high levels of oestrogen and progesterone, which are produced in
pregnancy. Certain drugs such as those to prevent malaria can lighten hair, while some epilepsy
medications can darken it.
Blond children tend to see their
hair darken around age 7 or 8. The mechanism for this is unknown and probably not
related to hormones, as the darkening precedes puberty by a number of years.
New parents often find the first
coat of their baby's hair is darker than expected. It is not until this first
hair is shed and replaced, at about eight to 12 months of age, that you get a
clear indication of their hair color.
Growth
Human hair growth is cyclical.
During the anagen phase, hair grows continuously at a rate
of 1 centimeter per month. Anagen can last three to five years on the scalp and
produce hair that grows to between 36 to 60cm in length.
At the end of the anagen phase, the
follicle turns off and hair growth stops and remains off for three months.
Toward the end of this resting (telogen) phase, the hair is shed and the
follicle remains empty until the anagen phase of the cycle restarts.
Pigment production also turns on and
off in rhythm with the hair cycle. When pigment cells turn off at the end of
one hair cycle and fail to turn back on with the onset of the next, hair
becomes gray.
Losing
color
Genetic factors appear to be
important in determining when we turn gray. Identical twins seem to go gray at
a similar age, rate and pattern, however we're yet to identify the controlling
genes.
There is no evidence to link the
onset of graying to stress, diet, or lifestyle. Certain autoimmune
diseases such as vitiligo and alopecia areata can damage pigment cells and
induce graying. However, these conditions are uncommon and can explain only a
tiny fraction of graying.
Early graying occurs in premature
aging syndromes such as Hutchinson’s-progeria and Werner syndrome, where every aspect of aging in the body is
accelerated. Premature graying can also be seen in people affected by
pernicious anaemia, autoimmune thyroid disease or Down syndrome.
So, why doesn’t pigment production
turn back on?
At the end of each hair cycle, some
pigment-producing melanocytes become damaged and die. If the melanocyte stem
cell reservoir at the top of the hair follicle can replenish the bulb, this
keeps pigment production going. But when the reservoir of stem cells is
exhausted, pigment production stops and the hair turns gray.
Scientists have long known that to
prevent hair from going gray they would need to either prolong the life of the
melanocytes in the hair bulb — by protecting them from injury — or expand the
melanocyte stem cell reservoir in the upper or top region of the hair follicle
so they continue to replace lost pigment cells.
A group of French scientists have
identified a new series of agents that protect hair follicle melanocytes
from damage at the end of the hair cycle. This enables pigment production to
restart as soon as the next hair cycle begins.
The agents work by mimicking the
action of an enzyme called DOPAchrome tautomerase. This enzyme is the naturally
occurring antioxidant in the hair bulb that protects melanocytes from oxidative
damage. By duplicating the effects of DOPAchrome tautomerase, melanocyte
metabolism and survival improves.
The new agents are being formulated
into a product that can be applied as a spray-on serum or shampoo. But they
won't re-color gray hair or bring back the dead cells that produce hair color.
Instead, they protect your melanocytes.
So for those who cannot find it
within themselves to embrace the salt and pepper look, new options are on the
horizon.
This article was originally
published on The
Conversation. Read the original article.
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