Ed Yong in Not Exactly Rocket Science:
Think of all the adults you know. Think of your parents and grandparents. Think of the teachers you had at school, your doctors and dentists, the people who collect your rubbish, and the actors you see on TV. All of these people probably have little mites crawling, eating, sleeping, and having sex on their faces.
There are more than 48,000 species of mites. As far as we know, exactly two of those live on human faces. While their relatives mostly look like lozenges on spindly legs, face-mites are more like wall plugs—long cones with stubby legs at one end. They don’t look like much, and most of us have never looked at one at all. But these weird creatures are almost certainly the animals we spend the most time with.
They live in our hair follicles, buried head-down, eating the oils we secrete, hooking up with each other near the surface, and occasionally crawling about the skin at night. They do this on my face. They probably do it on yours. 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. If you want to find humanity’s best friend, ignore dogs; instead, swab a pore and grab a microscope.