Hair loss over time

The mere presence of the necessary genes and hormones for hair
loss isn’t enough to cause baldness. Susceptible hair follicles also
have to be exposed to the responsible hormones. The onset of hair
loss varies from one individual to another and is influenced by
genetic expression, the levels of testosterone and DHT in the
bloodstream, and age.
Hair loss doesn’t occur all at once, but is cyclical. People who are
losing their hair experience alternating periods of slow hair loss
and rapid hair loss, and even periods when hair loss stabilizes. The
factors that cause the rate of loss to speed up or slow down are
unknown.
Most men who have extensive balding develop much of it by age
30. Twenty-five percent of men will show clinical balding by age 30,
and half of the male population will show some degree of clinical
balding by age 45 to 50. Balding slowly continues into the next
decade or two, and then the process seems to slow down as men
approach 60 to 65. As this is a genetic process, it is probable that
the men who bald later in life rather than earlier also have a form
of genetic hair loss, just not the obvious process we see in the
younger men with classic pattern balding.
Men who continue the balding process well into their 30s and 40s
typically don’t lose their hair as quickly or as completely as men
who start balding in their early 20s. About 7 percent of men who
are balding develop the most complete form of balding (called the
Class VII pattern; see Figure 4-1), in which only the wreath of hair
exists around the head. Those men with Class VII balding patterns,
usually show those patterns before they reach 30 years old. This
wreath of hair is permanent hair in most men and measures about
21
⁄2 inches in the mid-back of the head when the balding process
reaches completion. Most men who show balding don’t advance to
full balding.
To make matters more confusing, the age of onset discussed above
reflects the majority of men, yet there are still some men who start
the process later in life (in their 30s, 40s, and even 50s).
The most common balding patterns are seen at the frontal hairline
where frontal and temporal recession occurs, moving slightly
upward toward the top of the head. A bald spot may appear in the
crown and when it does, it seems to widen slowly as men age.
Sometimes, the crown balding area merges with the frontal reces-
sion, clearing a wide bald channel in the center of the head that we
jokingly call the “runway.” Genetics determine the final pattern.