Hair graying is one of the most notable changes of aging. It is
often quoted that as a rule of thumb, 50% of people are 50% gray
by the age of 50 [28]. Recent epidemiologic studies of men and
women of various races suggests a far lower number-only 6–23% of
people have 50% gray hair at age 50 [34]. People ofAsian andAfrican
descent showed less gray hair than those of Caucasian origin [34].
The age of onset of hair graying is also influenced by genetics.
Much like the skin, the pigment of the hair shaft is derived from
specialized cells termed melanocytes, which transfer pigment, or
melanin, via organelles called melanosomes. However, unlike the
skin in which there is continual production of pigment, the activity
of the melanocytes surrounding the hair follicle is intermittent and
is tightly linked to follicular cycling. Hair pigmentation occurs only
during the growth, or anagen, phase which typically lasts 3–5 years.
With each hair cycle, various factors may impact the fidelity of hair
pigmentation. Studies have shown that gray hair is associated with
a decrease in follicular melanocyte population and a decrease in
melanin content [35]. A buildup of reactive oxygen species along
with a decreased ability to handle oxidative damage has also been
implicated in the process of graying [36–38].