causes hair loss?
There is much debate on this topic. While the
link between certain forms of hair loss and the immune
system is well-accepted, there is also evidence
for a connection between the immune system and
pattern loss (androgenic or androgenetic alopecia).
In line with this, it appears that male hormones--especially
DHT--trigger an autoimmune response in pattern
loss, initiating an attack on the hair follicle
that can be observed microscopically. This results
in destructive inflammation that gradually destroys
the follicle's ability to produce terminal hair.
The reason for this could be that androgens somehow
alter the follicle, causing it to be labeled
a foreign body. A possibly related factor is
that elevated androgens also trigger increased sebum
(oil) production, which can favor an excessive
microbial and parasitic population, also leading
to inflammation. In any case, hair progressively
miniaturizes under the withering autoimmune attack,
so that with each successive growth cycle it
shorter and thinner until it finally turns into
tiny unpigmented vellus hair (peach fuzz). In
men, balding typically follows the classic horseshoe
pattern known as male pattern baldness or MPB,
though diffuse thinning can also occur. It has
been noted that both the number of androgen receptors
and the level of 5-alpha reductase, which converts
testosterone to DHT, are higher in susceptible
areas than in the rest of the scalp. Women's
hair loss tends to be diffuse but is also primarily
hormonally driven. The story of balding is, however,
not the story of androgens alone. Rather male
pattern hair loss appears to have multiple causes.
damage to blood vessel linings can inhibit a
factor they ordinarily produce: endothelium-derived
relaxing factor (EDRF) or nitric oxide (NO).
Minoxidil probably works in part by mimicking
factor. Similarly it has been noted that severe
baldness is strongly correlated with heart disease
and even diabetes, so there appears to be some
common etiology outside of the strictly androgen
paradigm for male pattern hair loss. There are
likely other factors as well.