A healthy person’s body is teeming with microscopic life, both inside and out. Swathes of research have promoted the benefits gleaned from the microbiomes that exist in our guts, genitals, and elsewhere. The same invisible communities live on our skin and even our faces, including small arachnids from the genus Demodex such as D. folliculorum and D. brevis, who live in hair follicles and sebaceous glands respectively. The thought of having microscopic spider relatives embedded in your skin might seem a little daunting to an arachnophobe, but their presence is rarely a problem.
A paper published in PLOS ONE back in 2014 revealed that 100% of adults tested in their study had traces of DNA from at least one Demodex species. Demodex mites are microscopic at around 0.3-0.4 millimeters (0.012-0.016 inches) in length. Their small stature allows them to easily pack into your pores, with about one D. folliculorum per follicle and a few D. brevis per sebaceous gland. The average adult human body has roughly 5 million hair follicles, which gives you an idea of the potential for mite habitability.
These mites are harmless for the most part. Suppressed immune systems can lead to an overpopulation of mites, which can cause some inflammation and itchiness. There are also correlations to blepharitis (chronically inflamed eyelids), rosacea, and certain types of acne – but the vast majority of people will never even notice their mites. Regular good hygiene practices are often enough to keep them in check.
Analyzing these mites at the genetic level can tell us more than simply who is living on our faces, it can also yield information about their diversity and offer clues as to where and when these mites first began hitching a ride on humans. By conducting the same research in different regions of the world, we can establish if species are ubiquitous or if they have spread in specific geographical areas. "They tell a story of your own ancestry and also a story of more ancient human history and migration,” said Michelle Trautwein, an entomologist at the California Academy of Sciences in San Francisco who has studied Demodex, in an interview with NPR.
Collecting face mites for research is not an enviable process, requiring you to get up close and personal with the exudations of another person’s skin. Researchers can use tape or glue pressed against a person’s skin to pull them out, as well as plucking out hairs with tweezers or scraping the skin and collecting it for examination. Researchers in the PLOS one study squeezed participants’ noses in order to expel some sebum from their pores, which was then scraped up.
"I actually put glue on a glass microscope slide and stick it onto a person's forehead,” explained Trautwein. “Then I slowly peel it off. I look under a microscope for mites that are stuck in the follicles that stick up from the thin layer of skin that got peeled off.”
"It can be pretty addictive and exciting. It's sort of a meditative process of looking through this microforest of follicles and hairs and looking for just the right potential movement or shape."