Mites like the one pictured here are living, dying, and leaking poop on pretty much everyone's faces. So at least you're not alone.

Photo Credit: Joel Mills | CC BY-SA 3.0

We first told you about the bugs that take up residence inside your pores a couple years back, when researchers proposed that the critters – which usually populate our faces, living and eating and mating and dying there, more or less peacefully – might be problematic when present in great enough numbers. People with rosacea, for example, have been known to harbor ten times as many face-mites as those without. It is hypothesized that the bacteria found in mite-feces – which the mites, lacking anuses, release only once they've died and started to decompose – could exacerbate the inflammatory, tissue-damaging immune responses typical of the skin condition.


Just how common are face mites? According to more than 150 years of research on the two species known to reside in and on our faces (Demodex folliculorum and Demodex brevis): pretty damn common. But for all the science that's been done on mites and pores and poop and skin conditions, researchers have yet to perform a systematic assessment of the universality of face-mites. Until now.


Here's Ed Yong writing for National Geographic:

A group of scientists led by Megan Thoemmes and Rob Dunn at North Carolina State University found that every adult in a small American sample had face-mites on their faces—something that was long suspected but never confirmed... That, combined with over a century of other studies, strongly suggests that the mites are to faces as smoke is to fire. Or, at least, on adults. Thoemmes also sampled ten 18-year-olds and found Demodex DNA on just 70 percent of them. This fits with what earlier studies had shown—the mites seem to become more common with age. They're rare on babies, more common on teenagers, and universal in adults. No one really knows where we get them from. Dogs get their face-mites during nursing, and humans might do the same—after all, one study found a lot of Demodex living in nipple tissue. But the fact that some teens aren't colonised suggests that we pick up these creatures throughout our lives.


That Thoemmes and Dunn looked for traces of mites by scanning for DNA is significant. Previous studies have sought to identify mites visually, with a microscope, after plating a sample swabbed from a person's face. One problem with this method is that mites don't distribute themselves evenly across a person's face; just because your forehead swab turns up clean doesn't mean there aren't mites living on your chin.

Another issue: Just because there aren't any mites alive on your forehead today doesn't mean there weren't some wriggling there yesterday. Mites, after all, move. They also die. When they do, their bodies decompose, and their insides leak into your pores. The mites' parting gift is like a calling card, issued from beyond the grave, made of feces and – to the benefit of Thoemmes and Dunn's investigations – DNA.


Read more about the researchers' study, the results of which appear in the latest issue of PLOS ONE, over at National Geographic.