The secret life of mites in the skin of our faces

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The microscopic mites that live in human pores and mate on our faces at night are becoming such simplified organisms due to their unusual lifestyles that they may soon become one with humans, new research suggests.

The mites are transmitted at birth and are carried by almost all humans, with their numbers peaking in adults as the pores enlarge. They are about 0.3mm long, are found in the hair follicles of the face and nipples, including eyelashes, and eat the sebum naturally released by pore cells. They become active at night and move between follicles seeking to mate.

The very first genome sequencing study D.folliculorum mite found that their isolated existence and resulting inbreeding causes them to shed unnecessary genes and cells and evolve into a transition from external parasites to internal symbionts.

Dr Alejandra Perotti, associate professor of invertebrate biology at the University of Reading, who co-led the research, said: “We found that these mites have a different arrangement of body part genes compared to other similar species due to their adaptation to indoor sheltered living. These changes in their DNA resulted in unusual body characteristics and behaviors.

The in-depth study of Demodex folliculorum DNA revealed:

  • Due to their isolated existence, with no exposure to external threats, no competition to infest hosts, and no encounter with other mites with different genes, genetic reduction has caused them to become extremely simple organisms with tiny legs powered by only 3 unicellular muscles. They survive with the minimum protein repertoire – the lowest number ever seen in this and related species.
  • This genetic reduction is also the reason for their nocturnal behavior. Dust mites lack UV protection and have lost the gene that causes animals to wake up from daylight. They were also unable to produce melatonin – a compound that makes small invertebrates active at night – however, they are able to fuel their mating sessions all night long using melatonin secreted by human skin at dusk.
  • Their unique genetic disposition also results in unusual mating habits of the mites. Their reproductive organs have moved forward and the males have a penis that protrudes upwards from the front of their body, which means that they must position themselves below the female when mating and copulate both clinging to human hair.
  • One of their genes flipped, giving them a peculiar arrangement of more prominent mouth appendages for food gathering. This facilitates their survival at a young age.
  • Mites have many more cells at a young age compared to their adult stage. This contradicts the previous hypothesis that parasitic animals reduce their cell number early in development. The researchers say this is the first step for the mites to become symbionts.
  • Lack of exposure to potential mates who could add new genes to their offspring may have put the mites on a path to evolutionary deadlock and potential extinction. This has already been observed in bacteria living inside cells, but never in an animal.
  • Some researchers had assumed that the mites had no anuses and therefore had to accumulate all their excrement throughout their lives before releasing them when they died, causing inflammation of the skin. The new study, however, confirmed that they have anuses and have therefore been unfairly blamed for many skin conditions.

The research was carried out by the University of Bangor and the University of Reading, in collaboration with the University of Valencia, the University of Vienna and the National University of San Juan. It is published in the journal Molecular biology and evolution.

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

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Materials provided by Reading University. Note: Content may be edited for style and length.

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