More than 90% of us host 0.3 mm long mites in the oily folds of our face, most of them live in the pores near our nose and eyelashes. It is probably the closest relationship to another animal that most of us never knew we had. The mite, Demodex follicularum, spends its entire life staying in the pockets of our skin. During the day they feed on the oily secretions of our skin, at night they leave the pores to find a match and find new follicles in which they can have sex and lay their eggs. If the thought makes you want to wash your face, forget it. You have been carrying mites since you were born – they are transmitted from mother to baby during breastfeeding – and they live very deep in the pores to be flushed. And we need them, says Dr. Alejandra Perotti of Reading University, who co-authored the study. “We should love them because they are the only animals that live in our body all our lives and we should appreciate them because they clean our pores.” “After all, they’re cute,” says Dr Perotti. Maybe not everyone would agree. Mites have four pairs of rigid legs each with a pair of claws. Beyond that a long body like a worm that, under the microscope, can sometimes be seen protruding from the follicles of our hair. But this latest study, published in the journal Molecular Biology and Evolution, showed how incredibly familiar their relationship with humans has become. The researchers analyzed the mite genome and found that it has the smallest number of functional genes of any arthropod (insects, spiders and crustaceans). Animals have become so dependent on their human host that their genome is “eroded” – stripped of the bare minimum of genes needed to survive, the researchers concluded. They found that the gene that normally regulates wakefulness and sleep in arthropods has been lost. Instead, the body detects changes in the levels of the hormone melatonin in our skin secretions. It goes up when we sleep, telling Demodex to get up, and it goes down when we wake up – their motto to return to our fatty pores for dinner. They have also lost the gene that protects their body from ultraviolet light – what does it mean when you only go out at night? Even their body design is minimalist – each leg is powered by a single muscle cell. Their ecology, which is so closely synchronized with humans, shows that the species is on its way from parasite to symbiosis – an organism that depends entirely on another for its survival. In this case, we. As their genetic diversity shrinks and so does their ability to leave their host and find new mates, they are also in danger of extinction – either when humans do or as a result of a significant change in their environment. Demodex was once thought to be a cause of common skin conditions, but in healthy people the evidence that Demodex actually helps prevent problems such as acne by unblocking pores. But that’s not the only reason we should care about them, says Dr. Perotti: “We live in a world where we have to protect biodiversity – and these are our own animals.”
