WHAT CAUSES HAIR LOSS?
Hair loss is caused by a gradual miniaturization of the hair follicles under these influence of multiple complex biochemical pathways in genetically sensitive individuals. We know that males must possess the hormone Dihydrotestosterone (DHT) to have
hair loss. We know that castrated males will not loose their hair unless
exposed to exogenous sources of testosterone. We know that products which
retard the formation of Dihydrotestosterone delay the hair loss process and
sometimes temporarily reverse it. These products do not always work and their
affects do not appear to be permanent.
Affected AreasFortunately, only the top of the scalp is affected by
androgenic alopecia in typical male pattern baldness and the Ludwig pattern of
hair loss in women. The back and side are sparred. The hairs from the back and
sides can be moved to any region on the body and continue to grow. The hairs on
the top will still fall out no matter where they are move on the body. This is
the principal of "donor dominance" and means that the donor hairs retain their
characteristics no matter where they are relocated to. This is fortunate to
individuals seeking hair restoration surgery. We can transplant these
non-affected hairs to any part of the scalp and they will grow for the remainder
of a person life unaffected by the DHT.
InheritanceIndividuals inherit the gene for hair loss from either their
mother or father. Sometimes one must trace the gene far back in their family
history to identify the "culprit". Often times the gene may have come from
one's mother's, mother's, mothers, father. It is difficult to trace this sort
of inheritance because the gene for typical male pattern baldness does not
express itself in women. We tend to see typical male pattern baldness in women
who are exposed to exogenous sources of testosterone or those who have a
hyper-androgen state such as an adrenal tumor.
Hair loss does occur in women, however, but he pattern is different. We
typically call this pattern the Ludwig pattern of hair loss. There are other
patterns of hair loss in women particularly. One common pattern is the
generalized thinning pattern, which we call DUPA (diffuse unpatented alopecia).
Women who present with a Ludwig pattern or DUPA often have a family history of
hair loss from their mother.
While hair loss in men is stalled by Propcia (finasteride) it does not appear
to work in women. Rogaine (minoxidil) works in both men and women so it must
have a slightly different mechanism of action. All of these slightly different
patterns make the study of hair loss and its treatment rather complex. There is
still much we need to uncover in the science of hair loss for both men and
women.
Age of OnsetThe age of onset varies from one individual to another.
Men who begin to loose their hair at a younger age will typically have a much
greater degree of hair loss than men who begin loosing their hair later in
life. For this reason it is best for men to avoid hair restoration surgery at a
minimum until their 23rd birthday. Even then surgical solutions are far more
risky than with much more mature men. Well informed men less than 23 years of
age are sometimes candidates for hair restoration surgery, but the overall plan
should be much more conservative for these men.
In general, we insist the younger male knows that he has a limited donor
supply and that each transplant reduces that supply based on the size of each
procedure. We also insist that they know we may be able to cover only the
frontal region of the scalp and that a bare or very thin spot may be left in the
vertex and sides of the scalp. Some men first begin to notice hair loss in
their late 20s, 30s, 40s, or even 50s. With each decade the amount of
anticipated loss is less. Therefore, the older the onset, the more likely one
is to be an excellent candidate for hair restoration surgery.
Women may first begin to notice hair loss after a pregnancy. In fact, it is
common for a woman to notice hair loss three months after her delivery. This
loss is typically temporary and the hair may return to its original state about
one year later. If it does not return to normal, this is an indication that the
loss may be permanent. Even worse, the loss may become progressive. The
majority of women begin to loose their hair in the 5th decade of life. It is
generally progressive. Typically the hairline is retained with women and the
top thins. With time the amount of thinning progresses until more and more bare
skin is noticed.
Pathophysiology of hair lossDHT in sensitive males causes a premature
exfoliation of hair. We call this exodus effluvium. There are four cycles of
hair growth. The first is anagen or the actively growing phase. This phase is
about 2 to 5 years in duration. The second is catagen or the programmed rise of
the hair follicle into the upper layers of the dermis along with the cesstation
in growth. The third phase is telogen or a dormant time lasting about 3
months. In this phase the hair just sits. The fourth phase is exogen and is
marked by the falling out of the the hair. We believe that exogen is the result
of a new anagen cycle hair growing out of the scalp and pushing the dormant
telogen hair out of its path of growth. In androgenic alopecia a number of
hairs seem to go into telogen all at once.
Not all hairs in the follicular unit (typciall 2 to 4 terminal hairs per
follicular unit) are affected at the same time, but many hairs in different
follicular units are affected all at once. The hairs fall out in unison with
the exogen cycle. This results in a marked degree of thinning all at once.
This mass exogen cycle of hair tends to occur in waves. In other words, you
hair loss may appear stable for years, then all of a sudden it gets far worse.
If this were the only physiogic event, hair loss would not be extreme.
Unfortunately, the next event is the far more significant to the appearance of
"baldness". When the affected hairs resume growth with a new anagen cycle, they
do not regrow with the same hair diameter.
They appear finer, grow slower, have a longer telogen phase, a shorter anagen
phase, and have less pigment. Because hairs are cylinders and the volume of a
cylinde is dependent on the radius squared, a decrease in radius by 1/2 results
in a decrease in hair volume to 1/4th its original volume. A drop in volume of
this degree allows far more light to penetrate to the scalp, the scalp burns
more easily, and the hair loss process appears far worse. Gradually all the
hairs in a follicular unit are affected and the area changes from thin to bald.
All hairs remain, but they are fine, non-pigmented, slow growing vellus hairs
that give no coverage value and the patient now appears bald.
The difference in men and women appears to be the pattern of loss and the
response to various medications. Therefore, it is safe to say that the
pathophysiology is different for both men and women. There is much to study
here, but we already know that the number of androgen receptors in the frontal
scalp of women is less and that the amount of aromatase activity in the
frontal scalp of women is greater.
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