The Mites That Live and Breed on Your Face Have Anuses, Genome Study Finds

The mites that live and breed on your face have anus, genome research shows

Scientists have finally unraveled the genetic secrets of humanity’s coziest roommates: Demodex folliculorum, also known as skin mites. The findings confirm, among other things, that these mites do have anus, contrary to previous speculation. They also indicate that the microscopic animals may not be as potentially harmful as often thought and that they are evolving into interdependent, symbiotic creatures that could provide us with some more benefits.

D. folliculorum is actually one of the two mites species who call us home, along with Demodex brevis. Both species are arachnids – more closely related to ticks than spiders – but D. folliculorum mites are the ones that usually reside (and mate) on our faces. These stubby worm-shaped critters live for two to three weeks, all the while embedded in our pores, clinging to our hair follicles and feeding mainly on our sebum, the oily substance supplied by our bodies to protect and moisturize the skin.

Despite virtually every person in the world having their own collection of mites, there is still a lot we don’t understand about them. But in a new study published Tuesday in the journal Molecular Biology and Evolution, researchers in Europe say they can now analyze the genome of D. folliculorum — a feat that could answer some lingering questions about their inner workings.

For example, some researchers have claimed that these mites do not have an anus. Without an anus, the theory goes, their fecal waste simply accumulates inside them for their short lifespan and isn’t released until they die. Some have also speculated that an overabundance of mites can cause a skin condition known as rosacea, perhaps due to bacteria released in this explosion of poop following the death of a mite. However, other research has questioned that claim, and the researchers behind the new study say they have confirmed that mites do indeed have an anus.

Study author Alejandra Perotti, a researcher at the University of Reading in the UK, notes that the increased presence of mites in people who develop rosacea and other skin conditions may very well be a result of the condition and not the actual cause. And if mites don’t leave huge amounts of poop when they die, there’s a less obvious reason why they’d make us sick. Other studies, for what it’s worth, have continued to find a connection between the mites and rosacea, although they may be just one of them many triggers involved

“It’s easier and faster to blame the mites,” she said in an email to Gizmodo.

The team’s other findings show that these mites have evolved to be incredibly lazy, genetically, as a result of hooking up their wagon to humans. They have a very simple genome compared to other related species, and they seem to survive on the bare minimum of cells and proteins needed to function (their leg pairs are even powered by a single muscle cell each). They are no longer able to survive exposure to ultraviolet light, which explains why they crawl deep into our pores and only move and mate at night, and they don’t even seem to produce their own melatonin like many animals do — in instead they seem to be moaning about us. They are also passed on from mother to child, often through breastfeeding, meaning populations have relatively low genetic diversity. And their lack of natural enemies, host competition and general sheltered existence suggests that the mites will likely only lose more genes over time.

The researchers theorize that these trends could one day lead to the end of D. folliculorum mites as a separate entity — a process that has been observed with bacteria, but never with an animal, they say. Ultimately, the mites may no longer live externally on our skin as parasites, but instead become completely internal symbiotes. If so, we may be seeing the very beginning of that transition happening now, although this transformation is unlikely to be complete for a long time to come.

Regardless of the future fate of these mites, the scientists say they may now be doing something good for us. For example, they can help clear the skin of excess dead cells and other materials, at least if their populations are kept in check. Perotti also hopes their research will give people “good knowledge of these permanent companions, who have been blamed for our skin problems for too long.”

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