Explaining face mites

The new online publication Vox is running an explainer about the species of face mites that live in your skin: “These mites live on your face and come out to have sex at night”.

Follicle mite drawing, from Wellcome Images
The follicle mite (Demodex folliculorum). Pen and ink drawing by A.J.E. Terzi, ca. 1919. Wellcome Images ICV No 23033 CC-BY 4.0

OK, let’s face it. There is no way to come up with a less creepy headline than that.

Your body harbors at least two closely-related species of mites: Demodex folliculorum and Demodex brevis. Both live in your hair follicles, but folliculorum live in the follicles' main cavity, whereas the smaller brevis live in something called the sebaceous gland, which secretes a waxy oil called sebum — likely the mites' main food source.
Both types of Demodex are densest on the face — especially near the nose, eyebrows, eyelashes, and hairline — but they live anywhere on your body where hair follices are. Scientists, however, have never fully studied the total abundance of mites on the human body. Dan Fergus, a researcher that works with [Holly] Menninger, estimates that the average person has between 1.5 and 2.5 million mites, but no one really knows.

Face mites are mostly benign. You don’t notice them and they just live off of sebum emitted by your glands. Their life cycle is only around 24 days, so they are constantly growing, mating and laying new eggs. They don’t even poop; they just keep their feces all bottled inside until they die.

Admittedly that doesn’t sound entirely benign.

The entire article is pretty interesting, and points to the “Meet Your Mites” project from North Carolina State University, one of the projects covered in the “Your Wildlife” site managed by Holly Menninger and Rob Dunn. The project has the goal of sampling a wide diversity of different populations to uncover relationships among the face mites.

There is every chance that they will find unexpected diversity. Really we know very little about the diversity of mites in other species of primates. There have been reports of follicular mites in macaques and a few other species of primates but apparently no systematic sampling of wild primates. And of course it’s possible that mites from other species of animals have colonized people since we domesticated them – or that human mites have colonized our domesticates.

Ed Yong has a great review of face mite biology from a few years ago that is worth reading if you want to find out more.