When
faced with the fact that there
are ten times more microorganisms than human
cells in your body, “bacteria” is perhaps the first
thing that comes to mind. However, we are also
hosts to a wide variety of microscopic mites. Mites
of the genus
Demodex
(Demodecidae) were first
discovered in 1842 in human earwax; but we now
know that there are two species of mites that dwell
on our faces:
Demodex folliculorum
and
D. brevis
,
with an average population density of around two
mites per eyelash. In 2014, it was found in a study
that every single human subject studied tested
positive for
Demodex
DNA. That’s right. They are
likely universal human associates.
Scientists have yet to determine what role
these mites play on the microbiota associated with
our face. Whether they consume dead skin cells
or facial sebum is part of the mystery as well, and
examining the mite’s guts might provide insights
to their diet. More disturbingly, however, is the fact
that these mites have no way of expelling waste.
Instead, they ‘hold it in’ throughout their lifespan
of 18-24 days. Upon death, their bodies dry out on
the face, leaving behind the built-up waste, and
an expulsion of bacteria.
Before you freak out and make a beeline for
a chemical peel, rest assured that these mites are
very common among humans and can appear
shortly after birth. Mite population increases as
their food supply rises, and their numbers increase
significantly during puberty of the human host. The
elderly are also more likely to be infested, with 84%
of the population affected at age 60 [1,2].
So far, no known harm to humans
has been explicitly proven,
particularly when
mite populations are in check. Nonetheless,
people who suffer from the skin condition rosacea
have reportedly ten times more
Demodex
mites
on their skin than an average person. Additionally,
an infestation of
Demodex
is associated with
blepharitis, an unsightly inflammation of the
eyelids [2]. However, the direct causation of these
afflictions is difficult to prove.
These mites may have been acquired long
ago, starting from our hominid ancestors. In one
study, mites collected from Chinese populations
were found to have distinct genes from those
co l l ected f rom Nor th and South Amer ican
populations [3]. Understanding these differences
can provide clues to the migration patterns of our
ancestors, revealing early interactions between
human populations. Due to its lengthy history in
association with humans,
Demodex
may shed light
on the evolution of the human immune system,
which helps us shape our response to diseases.
If you are still disgusted by these mites despite
the potential benefits of studying them, you might
be glad to know that there are therapies to get
rid of
Demodex
. Unfortunately, the sad news is
that you can never fully be rid of them as they
will eventually recolonise your face after about
six weeks. They are easily picked up from other
people in close contact or from sheets, pillows and
towels. It looks like face mites are here to stay!
