What’s eating you? Thoughts on Demodex, the eyelash mite
As a preface, I should mention that I am a foul creature. I’m not really any more filthy than the rest of you scum – I shower almost every day! – but I am obsessed with my own filth. This obsession manifests itself in different ways. For example, I regularly take note of how much trash I create through sloth and excessive packaging, which could be beneficial in helping me reduce waste. Mostly it makes me feel like trash myself.
But it also shows up in perhaps strange ways. (I don’t typically think it strange, but my friends see it as an “eccentric” characteristic so maybe I am a huge weirdo.) For example, I use pore strips not to clean my pores, but rather to look at all the gunk that was stuck up there. “Gross! Cool! Look at all that stuff that was jammed into my face!” I am fascinated by all the body cleanse hoaxes (despite my knowledge that they don’t work), like ear candles vacuuming out earwax, because I would love to be able to visualize my own filth.
It also has led to a complete comfort with the various invisible creatures that inhabit my body. No, comfort is not a strong enough word: more like straight adoration. I love my microbes! I’m so proud of my parents for allowing me to eat so much dirt as a child! Carl Zimmer’s NYTimes article about the fecal transplant brought me great joy (paper here), and I’ve used it to amuse at endless dinner parties. (I go to dinner parties?)
And while the wild and wacky world of intestinal flora will always be cool, I often think about what is living on the outside of our bodies. We must have some flea or mite or otherwise crawler that lives on our skin. But how do I even find out that sort of information? (The google search for “human parasite” doesn’t work so well.)
When I was visiting friends in New Orleans in February, a tropical diseases student, Rebecca, called me over: “OMG Hannah, come here, I have to show you something, you’re going to LOVE IT!” (Shows a little bit about my reputation.) She proceeded to show me pictures of Demodex spp. To say I screamed and ran in circles with joy would be an understatement.
The first Demodex specimen was collected in 1841 from a human ear canal and was initially described as a tardigrade. (They both look pretty cuddly – you can see images here.) It was placed in its own genus in 1843 by Richard Owen, the same guy who brought us Archaeopteryx, the word “dinosaur” and the concept of homology. Demodex means “lard-boring worm.” How cute!!
Demodex includes 65 species, two of which inhabit human skin: D. folliculorum and D. brevis. The rest inhabit basically every other species of mammal: I saw literature on hedgehogs, alpacas, koalas, bears, along with the usual cats and dogs. They bury themselves head-down into a hair follicle, with their tails sticking up, and feed on dead skin and oils built up in your pores. That’s right, your pores. Infants rarely have Demodex specimens, but almost all elderly people have them. They are considered the most common human ectoparasite, and 50% of adults harbor these guys.
So on your face and in your hair you probably have a healthy population of crawly little mites! They can aggravate disease, but it hasn’t been proven that they actually cause any dermatological disorders. They mostly just clean up your face for you. But it will make you think differently when you borrow a friend’s pillow, or crash on a communal couch.
It is pretty weird to think that there is an organism that evolved to live on my face, lay its eggs in my pores, feed on my filth. Maybe I should be more careful next time I use pore strips, as to not dislodge any of my little friends.