Imma Perfetto
Cosmos science journalist
If you didn’t already know, there are tiny parasitic mites living in our skin.
They live in the pores on our face (and nipples!) and come out only at night – moving between hair follicles in their quest to find a mate. Horrific.
Now, the first-ever full genome sequencing study of these mites (Demodex folliculorum) has revealed the genetics behind why they have such bizarre mating habits and body features, and how they might just be heading towards living within our tissues instead.
The new research has been published in the journal Molecular Biology and Evolution.
“We found these mites have a different arrangement of body part genes to other similar species due to them adapting to a sheltered life inside pores,” says co-lead author Dr Alejandra Perotti, associate professor of Invertebrate Biology at the University of Reading, UK.
“These changes to their DNA have resulted in some unusual body features and behaviours.”
For instance, males have a penis that protrudes upwards from the front of their body, so they must position themselves beneath the female – as they both cling on to a human hair follicle – to mate.
Best not to think about the party happening on your face every night as you sleep.
These simple creatures might keep getting simpler
The microscopic eight-legged mites are carried by almost every human. Passed on to us during birth, their numbers peak in adulthood as our pores grow larger.
Inside the pores they eat sebum, an oily, waxy substance that coats, moisturises, and protects your skin that is released by the sebaceous glands there.
Thankfully, since they’re only 0.3 millimetres long they’re too small to be seen with the naked eye; this is very fortunate for us, since living in and on hair follicles apparently also includes our eyelashes.
The mites’ isolated existence inside our pores has resulted in a lack of exposure to any external threats, zero competition to infest hosts, and no encounters with other mites containing different genes.
This has meant they’ve become extremely simple organisms. And according to the authors, the lack of exposure to genetically diverse mates may have set the mites on course for an evolutionary dead end, and potential extinction.
This has been observed in bacteria living inside cells before, but never in an animal.
The researchers say an indication of a first step towards becoming symbionts is that the mites have many more cells at a young age compared with their adult stage. This contradicts a previous assumption that parasitic animals instead reduce their cell numbers early in development.
The mites might not actually be causing skin conditions
A shrinking genome also explains why the mites only become active at night: they’ve lost the genes that make it possible to protect against ultraviolet (UV) radiation and to be awakened by daylight.
Not only that, but they’re unable to produce melatonin. While melatonin usually makes small invertebrates (animals without a spine) active at night, the mites fuel their all-night mating sessions using the melatonin secreted by human skin at night.
Some researchers had previously assumed the mites didn’t even have an anus and must accumulate their faeces throughout their lifetimes before releasing it all when they die, causing skin inflammation.
But this new study has confirmed they do in fact have anuses and have been unfairly blamed for many skin conditions. Somehow, I’m not that sympathetic.
“Mites have been blamed for a lot of things. 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,” says co-lead author Dr Henk Braig, a researcher from the school of Natural Sciences at Bangor University in the UK and the National University of San Juan in Argentina.
