Every single one of you – 100 percent of you reading this right now – has face mites. Before you break out the exfoliating scrubs and disinfectant, it's completely normal to have little animals living on your skin. And your pore pets are cute! Look at it wiggle its wee stubby legs!
New research suggests that no matter how scrupulous your personal hygiene, you still have face mites in your pores. Specifically:
"Within our samples, 100 percent of people over 18 years of age appear to host at least one Demodex species, suggesting that Demodex mites may be universal associates of adult humans."
Ubiquity and Diversity of Human-Associated Demodex Mites. August 27, 2014. PLoS ONE 9(8). Thoemmes MS, Fergus DJ, Urban J, Trautwein M, Dunn RR. doi:10.1371/journal.pone.0106265
Humans are big, sweaty, oily mammals. We contain niches (literal and figurative) in which organisms live and evolve. Our network of skin caverns offers food and shelter to two different species of mites: Demodex folliculorum and Demodex brevis.
D. brevis is slightly shorter and rounder, and spends most of its life nestled deeply inside a hair follicle sebum (oil) gland. D. folliculorum live more shallowly in the hair follicle, and occasionally take an evening constitutional walk around your face to see what's going on in the outside world and find greener hair follicle pastures. Oh, and to look for a mite hookup and lay eggs.
Typically there is only one brevis mite per sebaceous gland, and three-six folliculorum mites per hair follicle. Since you have 5 million hair follicles on you.... OK, perhaps that isn't as reassuring a factoid as I had hoped.
We've known about these mites for over a hundred years; they were first described in 1842. They are, aside from a weak correlation with rosacea, completely harmless. What these mites do and how we got them, though, is only beginning to be understood.
Meet Your Mites
The Dunn lab at North Carolina State University studies the ecosystems of our bodies. Their Belly Button Project, for example, looked at the diversity of bacteria found in our navels.
Hundreds of people over the last few years have filled out long release forms at the North Carolina Museum of Natural Science, and lined up to have their faces examined. I'm a willing participant; in 2013 I had my face scraped by scientists from this face mite project. Here's a gallery of face mites from scientists and science writers from all over the world.
There are a lot of different ways to collect mites; using plain old scotch tape works reasonably well, but hair plucking and scraping also is used. This group of researchers gently "expressed sebum from follicles." It's a bit like squeezing a zit, and then scraping up what comes out with mineral oil and a spatula.
A paradox of interest to the researchers was a discrepancy between how many people have living mites collected from their faces, and how many living mites are collected on cadavers. Over the last 100 years, scientists have been steadily scraping faces of both live and dead people, and the numbers remain remarkably consistent.
About 20 percent of living people who had non-invasive sampling of their face have living mites collected. Cadavers, more tolerant of rough facial sampling and eyelash plucking, all contain live facial mites – 100 percent of corpses. (There is a remarkably long and rich history of cadaver facial mite sampling. Sadly, most of these studies date from 1908-1933, which means I can't ask how one finds 100 dead people to sample, and then WHY.)
The researchers then looked for DNA from mites in a sub-sample of 19 individuals over 18, and a second group of 10 individuals that were 18 year-old teenagers. 100 percent of the adults sampled in their research had mite DNA collected from their skin, which suggests we all have mites living on us–they just aren't effectively collected with tape or gentle scraping.
In the young adult group, only 70 percent had mite DNA on their skin. This is consistent with historical sampling results as well. You aren't born with these mites; baby nuzzling helps inoculate our offspring and keep the mite populations growing. As teens and young adults "nuzzle" each other, that also spreads the mites around.
Though this new research has a small sample size, it adds to a large number of studies that conclude mites are in your pores, having sex, right now.
Although, not pooping on you. Neither species has an anus; they just store up all the poop until they die. After death their grip relaxes and they are released onto the surface of your skin; their DNA and waste joins the oily layer keeping your epidermis moisturized.
But Wait, There's More
Once the researchers had genetic information about the mites, as well as geographic information about their hosts, they could start to answer some questions about just how related we and our mite populations are.
The two different mite species are not close relatives, and appear to have been acquired from different hosts in our evolutionary past. D. brevis is more closely related to dog mites than the D. folliculorum mites they share hair follicle space with.
Geographic variation in mite diversity was also unusual; D. brevis mites of people in China, North, and South America were far more genetically diverse than D. folliculorum mites. This matches the biology of the two species pretty well. The larger folliculorum species is more gregarious and active, so mixes up its genes more often. The smaller brevis species is more isolated, so mutations and genetic drift accumulate as genetic variation in isolated little pore populations. The variation also seems to echo our human genetic history; as human populations split and diverged 40,000 years ago, so did our mite lineages.
This is the first paper to come out of the face mite project; researchers hope to further investigate the genetic relations between humans and our mites. Our tiny little hitchhikers could tell us a great deal about human history.
You Contain Multitudes
I know the reaction of a lot of people to this news will be a bit like the photo at right; mixed horror and wonder. Embrace the wonder! Human bodies are amazing; from the dense rainforest habitat of our groins and armpits to desert wastelands of elbows, we are an ecosystem.
Why not re-assess how you view the collection of meat that carries you through the day, and love the one you're with. Including all the face mites, yeast, and bacteria on your animal self.
