The secret life of the mite in the skin of our faces

Image showing Demodex folliculorum mite on the skin under a Hirox microscope. Credit: University of Reading

Microscopic mites that live in human pores and mate in our faces at night are becoming such simplistic organisms, due to their unusual lifestyle, that they may soon become one with humans, new research has found.

The mites are transmitted during birth and are carried by almost all people, with the number peaking in adults as the pores grow larger. They are about 0.3 mm long, are found in the hair follicles of the face and nipples, including the eyelashes, and eat sebum that is naturally released by the cells in the pores. They become active at night and move between the follicles to mate.

The first ever genome sequencing study of the D. folliculorum mite found that their isolated existence and resulting inbreeding cause them to shed unnecessary genes and cells and move toward a transition from external parasites to internal symbionts.

Dr. Alejandra Perotti, associate professor of Invertebrate Biology at the University of Reading, who led the research, said: “We found that these mites have a different arrangement of body subgenres than other similar species because they adapt to a sheltered life. These changes in their DNA have resulted in some unusual body features and behaviors. “






Demodex folliculorum mite under a microscope walking. Credit: University of Reading

The in-depth study of Demodex folliculorum DNA revealed:

  • Due to their isolated existence, with no exposure to external threats, no competition to attack hosts and no encounters with other mites with different genes, genetic reduction has made them extremely simple organisms with tiny bones driven by only 3 single-celled muscles. They survive with a minimal repertoire of proteins – the lowest number ever seen in this and related species.
  • This gene reduction is also the cause of their nocturnal behavior. The mites lack UV protection and have lost the gene that causes animals to be awakened by daylight. They have also been unable to produce melatonin – a compound that makes small invertebrates active at night – but they are able to nourish mating sessions throughout the night by using the melatonin secreted by human skin at dusk.
  • Their unique gene arrangement also results in the mite’s unusual mating habits. Their reproductive organs have moved anteriorly, and the males have a penis that protrudes from the front of the body, which means that they have to place themselves under the female when they mate, and mate while they both cling to human hair.
  • One of their genes has reversed, giving them a special arrangement of mouthpieces that protrude specifically to collect food. This helps their survival at a young age.
  • The mites have many more cells at a young age compared to the adult stage. This counteracts the earlier assumption that parasitic animals reduce cell numbers early in development. The researchers claim that this is the first step towards the mites becoming symbionts.
  • The lack of exposure to potential mates who can add new genes to their offspring may have set the mites on course for an evolutionary dead end, and potential extinction. This has been observed in bacteria that live inside cells before, but never in an animal.
  • Some researchers had assumed that the mites do not have an anus and therefore have to collect all the feces through the waist before releasing it when they die, causing skin inflammation. However, the new study confirmed that they have anus and therefore have been wrongfully blamed for many skin diseases.
  • The secret life of the mite in the skin of our faces

    The picture shows an unusually placed penis of a Demodex folliculorum mite. Credit: University of Reading

  • The secret life of the mite in the skin of our faces

    Microscope image of the posterior end of the anus of a Demodex folliculorum mite. The presence of an anus on this mite had been mistakenly overlooked by some earlier, but this study confirmed its presence. Credit: University of Reading

The research was led by Bangor University 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-author of Bangor University and the National University of San Juan, said: “Mites have been blamed for many things. The long association with humans may indicate that they may also have simple but important beneficial roles. to keep the pores of the face disconnected. ”


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More information:
Gilbert Smith et al, Human follicular mite: Ectoparasites become symbionts, Molecular biology and evolution (2022). DOI: 10.1093 / molbev / msac125

Provided by the University of Reading

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