|
Why
do some people have more extensive hair loss than others?
Recent research suggests that there are differences in the concentration
of enzymes such as 5 alpha reductase in the skin and hair follicles
of people who have androgenetic alopecia (Sawaya 1997). Some people
seem to make much more of these enzymes than other people. It
is possible that people with higher concentrations of 5 alpha
reductase convert more of the testosterone to potent dihydrotestosterone
and this may cause more extensive androgenetic alopecia.
Research also suggests that there are differences in the sensitivity
of the hair follicle androgen receptors of people with hair loss.
The suggestion is that the greater sensitivity of androgen receptors
in some people means a certain concentration of androgens in one
person make promote much more hair loss than a similar androgen
concentration in someone with less sensitive androgen receptors.
If
androgens circulate in the blood stream, why is hair loss only limited
to the top of the scalp?
It is clear that the type of response the hair follicle makes
to androgens is predetermined during embryological development.
Moving hair follicles by hair transplantation does not alter the
response a hair follicle makes to androgens. Those hair follicles
fated to miniaturize in response to androgens will do so regardless
of what position on the body they might be moved to. Correspondingly,
those hair follicles that proliferate in response to androgens or
are androgen independent (take no notice of androgen activity) will
continue to grow regardless of what area of skin they are in. This
is very fortunate for the hair transplantation industry. Hair transplantation
simply takes healthy follicles from the back of the scalp that are
androgen independent and puts these follicles in the bald regions.
No matter how much androgen hormone is present the transplanted
hair follicles will continue to grow because they were fated to
do so during embryological development. The factors that determine
the response to androgens reside within the hair follicle. It has
been shown that dermal papilla cells from pubic hair follicles have
a far greater number of androgen receptors on their cell surface
than dermal papilla cells taken from beard hair follicles.
While androgens can reduce the time period of the anagen growth
in scalp hair follicles they can actually prolong anagen hair growth
in body hair. In addition, the action of the same androgens on the
same hair follicles but at different ages can have different effects.
For example, androgens promote the development of pubic hair in
teenagers, but by early twenties the rate of pubic hair growth is
declining. Chest hair growth gradually increases under the influence
of androgens to reach a peak of activity in our forties and fifties.
So different types of hair follicle respond differently to the same
androgen receptor binding trigger.
Why
do hair follicles on the top of the scalp respond to androgens with
hair loss whereas beard/chest hair responds with hair growth?
Not all hair follicles are created equal. As described elsewhere
the number of androgen receptors on the cells of a hair follicle
can vary quite considerably depending on the position of the hair
follicle on the skin surface. While hair follicles on the top of
the scalp are androgen sensitive and respond by gradual development
of androgenetic alopecia, hair follicles of the beard, chest and
upper back respond to the same androgens with accelerated hair growth.
Hair follicles elsewhere as on the arms and legs may not be sensitive
to androgens as they have few or no androgen receptors. So, the
differences in how scalp and non-scalp hair follicles respond involves
several factors.
- 1) Hair follicles that proliferate in response to androgens
such as beard and pubic hair have been shown to produce mitogenic
factors such as IGF-1. These factors apparently promote further
hair growth.
- 2) The metabolism of testosterone changes with hair follicles
from different regions of the body and different people. Males
with a reduced production of 5 alpha reductase have little beard
growth and often have hair growth with female characteristics
in the pubic and chest area.
- 3) In response to androgen binding of androgen receptors beard
cells secret a mitogenic factor to which only beard cells respond
and beard cells produce more stem cell factor than the scalp.
- 4) Androgens act on mesenchyme derived cells which in hair follicles
means the hormones act on the dermal papilla cells at the base
of the hair follicle. There is a greater concentration of androgen
receptors in pubic hair follicle dermal papilla cells. A lower
concentration in the in the beard dermal papilla and an even lower
number of androgen receptors in scalp hair follicle dermal papilla
cells.
What
is the most common form of hair loss affecting over 95% of men and
80% of women?
The hair line of adult man is higher than that observed in a boy
or teenager. This is due to limited frontal recession of the hair
line. This recession develops in more than 95% of Caucasian men
regardless of any further hair loss that may or may not develop.
Black and Asian men sometimes find their frontal hair line is preserved
while hair loss on the top of the head gradually progresses. This
is in contrast to Caucasian males. Recession of the adult male hair
line may be related to an androgen based alopecia but it does not
seem to be true androgenetic alopecia.
In the same way about 80% of women also have limited diffuse hair
loss in the front hair line especially the bitemporal regions. The
diffuse loss is not so obvious for women as for men and the onset
occurs later in life from mid twenties onwards. Unlike the frontal
hair loss in men, women retain their original teenage hair line,
there is simply diffuse loss in the front. As for men, this very
common form of hair loss seems to be related to a mechanism similar
to androgenetic alopecia.
What
are these pimples I can scratch out of my head that sometimes have
hair attached?
The pimple is probably hardened sebum. It is white or light yellow
in color and if pressed hard can be squashed and molded. The sebum
is made up of oils and material from the sebaceous gland attached
to the hair follicle and from keratinized cell debris. People with
many types of hair loss including androgenetic alopecia get these
pimples. An affected hair follicle that does not produce hair fiber
still has an active sebaceous gland and the hair follicle also still
produces sheath cell material. These products combine to make these
sebum plugs that you can pick out. Because the hair fiber is not
growing or not growing properly there is less force pushing this
stuff out of the hair canal so it can build up and form a sebum
plug. Sometimes hair follicles that still have hair in them also
make sebum plugs if the hair is not growing properly. Sebaceous
glands can also be androgen sensitive and may be promoted into increased
oil production. This can aggravate the problem with pore clogging
sebum. Regular washing and very mild shampoo might help but for
as long as the alopecia persists you will probably have these plugs
in some hair follicles.
|
