If you are eating, I wouldn't read this article.
Right now you most likely have little mites living and growing on your face. They look like this under a powerful microscope:
Yes, it's true. At least two species of mites live on human skin: Demodex folliculorum and Demodex brevis. They're usually just called eyelash or face mites, though they have been found in and on the ear canal, nipple, groin, chest, forearm, penis, and buttocks, too.
Each type of mite lives in different parts of our skin — D. folliculorum calls your pores and hair follicles home, while D. brevis hangs out in the deeper, oil-secreting sebaceous glands, according to BBC Earth.
These little eight-legged arachnids are closely related to spiders and live out their entire existence on our skin.
There's probably a lot of them on you. In a study of patients with rosacea, a skin-reddening condition that has been linked to the mites, researchers found hundreds in just a tiny 5-millimeter-wide square of skin. These numbers decreased when the patients were treated, so this is likely on the high end of mite density.
"It's hard to speculate or quantify but a low population would be maybe in the hundreds," study researcher Megan Thoemmes, of North Carolina State University, told BBC Earth. "A high mite population would be thousands."
A study published in the journal PLoS ONE in 2014 found that, in a small sample of 29 people, 100% of subjects older than 18 had mite DNA on their face (for 18-year-olds, the number dropped to 70%).
However, scientists could see mites under a microscope on only 14% of the people, likely due to the animals' nocturnal nature.
Each one lives about 14 days, five of which as adults. The males crawl out of your pores in the middle of the night, find females holed up in other pores, mate with them, and then crawl back. Females lay their eggs in their home pores.
They grasp on to you with a clawed palpus on each of their eight legs, and they eat the bacteria on your skin, dead skin cells, the oils you secrete, or possibly all three. (Researchers aren't entirely sure because, even though the mites are ubiquitous, they're still quite mysterious).
They can't poop, so they just fill up with feces until they die. The carcass then dries up and the dead mite — waste and all — breaks down on your face as other microorganisms living there feed on it.
The 2014 study also suggested that mites are transferred from mother to child while breastfeeding, since they are frequently found on nipple tissue as well.
That's probably not the only way they are transferred, though.
If you wipe out your Demodex colonies, they'll rebound in about six weeks, so it seems like they are picked up in many different ways — from contact with others and from things like towels and pillow cases.
This all sounds gross and horrible and you are probably itching right now, but these mites are typically harmless.
"I would think that they're not harming us in a way that's detectable," Thoemmes told BBC Earth. "If we were having a strong negative response to their presence, we'd be seeing that in a greater number of people."
Recent studies have suggested that people with rosacea have more of these mites, and that after successful treatment of rosacea people have fewer mites. So the mites and the bacteria that live in and on them could be the cause of the skin-reddening condition.
Yet some researchers think the condition is an inflammatory reaction their presence, while others think that rosacea is caused by unrelated skin changes. So the mites just proliferate more when the skin is inflamed, not cause the inflammation itself.
The mites have also been associated with acne and inflammation of the eyelids. But since everyone has them, they frequently show up when someone has a skin condition; their presence doesn't necessarily mean they are the cause.
Fascinatingly, since Demodex mites live on almost everyone, the Apollo moon walkers probably carried some along during their mission. Which means more face mites than people have probably visited the moon.
I'm going to go re-evaluate my life now.
