Saturday, October 6, 2012

Demodex folliculorum

           This little dude is tiny…microscopic…you wouldn’t even know it if he was right in front of your face. Or on it, for that matter.  These guys can live on the face of humans…in hair follicles, on eyelids, in eyebrows, on the nose or cheeks, and even in ear wax.  Some literature has reported finding these parasites in odd places such as on the scalp, penis, nipples, arms, chest, and even breasts.    Demodex folliculorum was first described by Dr. Jacob Henle, a famous anatomist, in 1841. It is generally accepted that under normal conditions, these mites aren’t harmful, in fact, they are sometimes regarded as commensals rather than parasites.  However, some people speculate that it may be responsible for various skin diseases based on the fact that increased numbers of these mites have been found on people who have conditions such as rosacea, perioral dermatitis, and blepharitis.  Causality has not been established (to my limited knowledge of the subject) for any of these diseases.

        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

An adorable little Demodex folliculorum
here to give you an 8-appendaged hug,
a smile, and a big thank you for all of the
food you've provided over the years...
especially when you were a teenager! Awwww!!!