Loss of hair

The presence of baldness genes and the hormone DHT (see
Chapter 4 for more on DHT and its role in hair loss) alone aren’t
enough to cause baldness. Even after a person has reached matu-
rity, susceptible hair follicles must continually be exposed to the
hormone over a period of time for hair loss to occur. The age at
which these effects finally manifest themselves varies from one
individual to another and is related to a person’s genetic composi-
tion and to the levels of testosterone in the bloodstream.
Although balding can start in men in their teens, it’s unusual to see
it much before the age of 17, when there appears to be a genetic
switch that starts the process. For example, a 15 year old may have
a full head of hair until, all of a sudden, he passes an age in the
later teens (usually between 17 and 19) and a genetic switch is
flipped on and he starts losing his hair.
Hair loss doesn’t occur all at once, nor does it occur in a steady,
straight-line progression. People losing their hair experience alter-
nating periods of slow and rapid hair loss and even note periods of
stability. Many of the factors that cause the rate of loss to speed up
or slow down are unknown, but it’s proven that with age, a
person’s total hair volume decreases.
Even if there’s no predisposition to genetic balding, some hairs
randomly begin to shrink in width and not grow as long as a
person ages. As a result, each group of hairs contains both full ter-
minal hairs and thinner hairs (similar to the finer hairs that grow
on the rest of the body), making the scalp look less full.
Eventually, some of the thinner hairs are lost, and the actual
number of follicular units may be reduced (for an explanation of
follicular units, refer to the earlier section, “How hair grows”). In
about one third of adults, even the hair around the back and side
of the head (the fringe area) gradually thins over time.
Fortunately, in most people, the fringe areas of hair retain enough
permanent hair to make hair transplantation possible — even for a
patient well into his 70s or 80s! In a small number of men, however,
the process of hair aging may start in the 20s or 30s, resulting in a
uniformly falling hair count. When this happens, transplantation is
more difficult because there’s not enough donor hair left to cover
balding areas.