popular theory is that infection of hair follicles by the Demodex
folliculorum parasite is correlated with pattern baldness. By
infiltrating the sebaceous gland of hair follicles the parasite
causes an immune response and inflammation of surrounding tissue.
Through long term invasion the parasite exhausts the hair bulb and
shifts the hair cycle from anagen to telogen. This theory is promoted
by certain companies that just happen to have a range of products
that kill off Demodex folliculorum! At least one of the companies
has conducted research that allegedly showed 88% of 240 men with
pattern baldness had Demodex folliculorum infection in their
hair follicles. There are several problems with this theory.
First, Demodex folliculorum infection is very common. Up
to 75% of the population, men, women, and children, have Demodex
folliculorum infection. However, there is a clear bias towards
men have pattern hair loss even though children and women are equally
susceptible to Demodex folliculorum infection. If Demodex
folliculorum infection was causing inflammation that pushed
hair follicles into telogen then one would expect to see some children
with pattern baldness and that women would be equally affected with
hair loss. Indeed, women have a stronger immune system and so one
might expect more women than men to have pattern baldness, but this
is not the case.
Second, research has shown that there are excessive numbers of
the Demodex folliculorum parasite in eyelash follicles. (Fulk
et al. Optom Vis Sci 1996 Dec;73(12):742-745). However, people with
pattern baldness do not lose their eyelash hairs.
Third, it would be impossible for hair follicle transplants to
work. Given thousands of transplant procedures are done every year
and 88% of men have Demodex folliculorum infection, then
most of the men with hair transplants must also have Demodex
folliculorum infection. In a hair transplant, follicles are
moved from the back of the head to the top of the same individual.
If the individual is infected with Demodex folliculorum one
would expect that the transplanted follicles would either already
be infected, or become infected in their new location. However,
transplanted follicles grow in every individual who has had the
procedure done and pattern baldness does not redevelop.
Fourth, there is evidence to show that pattern baldness is associated
with hair follicle inflammation for some people. However, studies
have been done to look at the effects of topical anti-inflammatory
solutions on pattern baldness. While the anti-inflammatory solutions
did reduce hair follicle inflammation they did not promote hair
Fifth, there is a widely available treatment to Demodex folliculorum
infection, pilocarpine gel. However, using this gel on the skin
does not promote any hair growth.
The more likely explanation for Demodex folliculorum infection
in men with pattern baldness is that the sebaceous glands of alopecia
affected hair follicles become larger and more active, producing
oils at a faster rate, under the influence of dihydrotestosterone
(DHT). The oils combine with dead cells from the hair follicle to
make sebum. The sebum is a rich source of nutrients and this is
the food that Demodex folliculorum eats. The oil food supply
increases in most hair follicles affected by pattern baldness so
these hair follicles can accommodate a greater number of Demodex
folliculorum parasites. Rather than the parasites causing pattern
alopecia, they simply take advantage of the increased food produced.
The parasite infection is a consequence of pattern baldness and
not a cause of the hair loss.