DNA study reveals surprises of mites living in our faces

(CN) — It's the creature no one wants to talk about — the Demodex folliculorum, a microscopic (0.3 millimeter) mite that lives in our faces. They come to live in facial hair follicles, eyelashes and even nipples when we're born, passed on from our mothers, eating the sebum released by cells in our pores. They mate at night, dancing between follicles while we sleep.

Now a team co-led by Dr. Alejandra Perotti of the University of Reading studied the DNA of the tiny mite and have discovered they're no longer external parasites: they are symbionts, living as a part of us.

In the study published Tuesday in the journal Molecular Biology and Evolution, Perotti and her team revealed the lack of external threats, competition and encounters with mites with different genes has led to the symbiotic relationship with humans. It's also changed them genetically: they've lost the genes that give them UV protection and cause them to produce melatonin. After all, they don’t have much reason to go outside of our pores — adapting to use melatonin secreted by human skin at dusk to help with nighttime mating.

“The moment they are not using some genes they will change or disappear, they do not need them anymore,” Perotti said in an email. “There are no selective pressures like predators, for example.”

The adaptations, however, may not be enough to save them. Because of how they go from person to person — from mother to child at birth — their genetic diversity is limited. In short, they're inbred.

“Because they are inherited from a few founder individuals, always from our moms, the population of a single human is highly inbred,” Perotti wrote, adding potential mates “of a different genetic background, bringing genetic diversity as the result of outbreeding is not possible.”

This, according to Perotti's team, has set the mites “on course for an evolutionary dead end and potential extinction."

Aside from a foreseeable end to the D. folliculorum mites, the study also dispelled one of the long-standing myths about the species.

Scientists had assumed the mites lacked an anus and released a lifetime of feces when they died, causing skin inflammation for their human host. But Perotti's team confirmed the mites do have anuses.

“Mites have been blamed for a lot of things,” said Dr. Henk Braig, co-lead author from Bangor University and the National University of San Juan. “The long association with humans might suggest that they also could have simple but important beneficial roles, for example, in keeping the pores in our face unplugged.”

Along with correcting this error, Perotti said she hopes everyone will have “the proper knowledge of these permanent companions, for our whole life, which have been blamed for too long for skin problems, and they are not the cause."

She added: "For those who did not know of the mites, it will be surprising to know that they are just these tiny companions just in front of the faces.”

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