This mite
is an animal belonging in the phylum arthropoda, which includes invertebrates
such as insects, spiders, shrimp, millipedes, and lobsters. Members of this phylum have jointed
appendages and chitinous exoskeletons.
(Chitin is a long-chain polymer derived from glucose that is found in the
cell walls of fungi as well as in the bodies of animals like mollusks and
arthropods.) Demodex belongs to subphylum chelicerata because it possesses
chelicerae rather than mandibles for mouthparts. It is in class arachnida which contains all
mites, as well as other animals such as ticks and spiders. It can be further
categorized into the subclass acari, which contains all living ticks and mites.
It used to belong to the large order
trombidiformes which has over 22,000 species representing 125 families of mites. Many mites in this order were medically
important or agriculturally important. However, that order has been split into two
orders in recent times and these mites are now found in the order Prostigmata.
(This taxonomic rank is what is accepted in the current literature, so I
thought I would put it here.) Demodex is in the family demodicidae, or
the “pore mites” family. There are many species of Demodex, but the two found in humans are D. brevis and D. folliculorum. The first one lives in sebaceous glands
connected to hair follicles, but we won’t be talking much about him today.
Today, we are looking exclusively at D.
folliculorum, which lives in hair follicles.
Life Cycle
When a boy mite and a girl mite
love each other very much…and their instinctive drives to reproduce overtake
them, they make babies. The males
actually do have a penis that exists between the first and second pairs of
legs, and the female has a vulva anus opening on her ventral side. After
mating, female mites travel to the base of hairs and lay their eggs inside of
the hair follicles. A female will lay anywhere from 20 to 24 eggs in a single
follicle. The larvae emerge from the eggs and have only six legs. The larvae feed on subcutaneous secretions until
they reach adulthood, which takes about 7 days. These larvae may have a role to
play in the formation of black-heads. When mature, the mites reproduce sexually
and the cycle completes itself. This
life cycle takes about 18-24 days to complete.
Who’s Got Mites on
Their Faces?
Virtually everyone has Demodex folliculorum living on them as
part of their normal skin fauna. The
distribution of these mites varies from person to person, and can have variable
impacts on individual health. Children
under 5 are almost never infected, but between 5 and 10 there is a 50%
infection rate. After the age of 10, the
infection rate spikes to a whopping 80%.
This is typically attributed to the onset of puberty, a time in which
sebaceous glands are producing oils in full swing. These oily secretions are food for these
mites, so since more food becomes available means that more mites can live in
one place. Thus an increase in infection. These infections can last throughout
life, with infection rates changing with age. About 25% of people in their
twenties are infected, and at age 50, that percentage jumps up a little to
about 30%. Finally, in our twilight
years, people age 80 to 100 have between 50%-100% infection rates. (The higher
rates are among populations of people in nursing homes.) There tends to be more
men who are infected than women in every age group…probably because men have
more sebaceous glands.
Diagnosis,
Prevention, and Treatment
Demodex can be found by taking a skin
scraping from the face and making a slide mount using mineral oil. Sometimes KOH is used to digest some of the
skin cells making it easier to find the little arthropods. Apparently, in extreme cases, a skin biopsy
may be taken for microscopic examination.
As the guy doesn’t usually cause any problems,
you don’t really have to prevent it so much as try to keep the numbers of them
in check. To do this, one should cleanse
the face twice a day with a non-soap cleanser, exfoliate from time to time to
remove dead skin cells, and avoid oil-based facial products and greasy makeup.
If your
doctor thinks that you have a skin condition related to this parasite, he or
she may recommend topical treatments such as crotamiton cream, permethrin
cream, metronidazole gel, or even oral ivermectin (severe cases).
Moral of the Story
Don’t
freak out about the fact that little mites are living on your face. After all,
they are there on other peoples’ faces too! It’s perfectly normal. But don’t
let that be an excuse to stop washing your face or wearing tons of makeup. You should still use common hygiene practices
to keep these guys from getting out of control whilst feasting on your facial
sebum. :P
Hahhaha... That cute drawing at the End was nice
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