The Secret Life of Mites on the Skin of Our Faces

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

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

Mites are transmitted during birth and are carried by nearly all humans, with numbers peaking in adults as pores grow. They measure about 0.3mm in length, are found in the hair follicles of the face and nipples, including the eyelashes, and eat sebum naturally released by pore cells. They become active at night and move between follicles looking to mate.

The first genome sequencing study of the mite D. folliculorum found that its isolated existence and the resulting inbreeding is causing the loss of unnecessary genes and cells and the 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 genes from body parts to other similar species due to adaptation to a sheltered life within These changes in their DNA have resulted in some unusual bodily characteristics and behaviors.”






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

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 encounters with other mites with different genes, genetic reduction has made them extremely simple organisms with tiny legs powered by just 3 unicellular muscles. They survive with the smallest protein repertoire – the smallest number ever seen in this and related species.
  • This gene reduction is also the reason for their nocturnal behavior. Mites lack UV protection and have lost the gene that makes animals wake up in 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 throughout the night using the melatonin secreted by human skin at dusk.
  • Their unique genetic arrangement also results in the mites’ unusual mating habits. Their reproductive organs have moved anteriorly, and males have a penis that juts up from the front of their body, meaning they have to position themselves underneath the female when mating and copulating while both cling to human hair.
  • One of their genes has reversed itself, giving them a particular arrangement of mouthparts that are especially protruding for gathering food. This helps their survival at a young age.
  • Mites have a lot more cells at a young age compared to the adult stage. This contradicts the earlier assumption that parasitic animals reduce their number of cells early in development. The researchers argue that this is the first step for the mites to become symbionts.
  • The lack of exposure to potential mates who could add new genes to their offspring may have put the mites on the path to 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 have assumed that mites have no anus and therefore must accumulate all of their feces throughout their lives before releasing them when they die, causing skin inflammation. The new study, however, confirmed that they have anus and were therefore unfairly blamed for many skin conditions.
  • The Secret Life of Mites on the Skin of Our Faces

    The image shows the penis in an unusual position of a Demodex folliculorum mite. Credit: University of Reading

  • The Secret Life of Mites on the Skin of Our Faces

    Microscopic image of the posterior end of the anus of a Demodex folliculorum mite. The presence of an anus in this mite has been erroneously ignored by some previously, but this study has confirmed its presence. Credit: University of Reading

The research was led 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 magazine Molecular Biology and Evolution.

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


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More information:
Gilbert Smith et al, Human Follicular Myths: Ectoparasites Becoming Symbionts, Molecular Biology and Evolution (2022). DOI: 10.1093/molbev/msac125

Provided by the University of Reading

Quote: The Secret Life of Mites on the Skin of Our Faces (2022, June 21) retrieved June 22, 2022 at https://phys.org/news/2022-06-secret-mites-skin.html

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