Re: Why does nose/eyebrow hair lengthen and hair develop on ears as we age?

This answer is from a postdoctoral fellow who did his graduate work on the 
FGF's (fibroblast growth factors) at UCSF.  They have been implicated in 
many developmental events, including the regulation of hair growth.

this is what he wrote to me:
Although my studies didn't focus on ear or eyebrow hairs, i may be able to
provide a little insight. As far as ear and nose hairs, we have hairs on
these parts of our bodies (and most other parts) all of our lives, but it
is the minuscule hairs that are only visible if you look real close. What
happens with age in some individuals is that the hair follicles that
produce these tiny hairs on the ears (and sometimes other body parts) are
transformed into a different type of follicle that no longer produces the
tiny hairs, but now produces the bigger and longer more visible hairs. What
is suspected of triggering this transformation are changes in the level of
hormones with age (e.g. facial hair follicles are transformed in this way
in response to testosterone - at puberty in males or later in life when
given to women who chose to become men). There are also familial cases of
patterned hair growth, but i don't think the genes have been identified
yet. As far as why hormone levels change with age, an endocrinologist would
probably be a more reliable source of information than moi.

In general though, i think this hair follicle transformation phenomenon is
poorly understood. (Note that the opposite transformation occurs in male
patterned baldness - the follicles that produce nice big long hair switch
to producing tiny hairs.) Why do just certain parts of the face and body
show these changes, why doesn't forhead hair become thick and long, for
example? Do forhead follicles not express a certain hormone receptor? Sure
genes are involved, but what regulates their expression is a fundamental
question that most developmental biologist would love to have the answers
for. Of course, there exists partial answers for the expression of some
genes that are expressed in follicles. The ones that i know about
(TGFalpha, FGF5, hedgehogs, keratins, agouti, etc), however, only seem to
play roles in hair follicle development and the production of hair, and not
necessarily in follicle transformations.

However, because there is big pharmaceutical money in hair research, we can
be hopeful that a more complete answer to the question may arise shortly.

Admin Note:  if you have access to a medical library, you might try look up the 
following review
 Ebling FJ, "The biology of hair." Dermatol Clin 1987 
Jul;5(3):467-81