Face mites are just half a millimetre long and not visible to the human eye, CBC science columnist Torah Kachur told Gill Deacon, host of CBC's Here and Now. "They're semi-transparent, they have eight legs, they kind of look like a tiny, in a way, see-through caterpillar."
Until recently, scientists thought that only a small proportion of the population had face mites.
However, a new study led by Megan Thoemmes, a graduate student in biology at North Carolina State University, found that 100 per cent of 253 people over age 18 sampled by her team had mite DNA on their faces, suggesting that the mites could be universal inhabitants of adult humans.
The study also found that human faces are home to two different species of the mites. The first is Demodex brevis, which burrows into our sweat glands.
"It's actually evolved the perfect shape to wiggle in the pores," Kachur said.
The other species, Demodex folliculorum, lives in hair follicles of our eyelashes, eyebrows and facial skin.
Thoemmes told Kachur that the mites collected from faces in different places, such as China and the Americas, can be genetically distinguished from one another, which makes them useful for tracing human populations and their migrations.