Most people are aware that their bodies are teeming with microscopic life, though that usually focuses on bacteria in the gut or all over the skin (including that cesspool we call a navel). However, less people realize that their skin is crawling with different species of mites: D. folliculorum that lives on their hair follicles and D. brevis that lives in their sebaceous glands. These mites aren’t insects, they’re arachnids. Not that having “microscopic spider-relatives embedded in your skin” is any more or less reassuring.
While previous studies have shown that only about 10-20% of adults have mites at any given time, a new paper published in PLOS ONE, led by Megan Thoemmes from North Carolina State University, has revealed that 100% of all adults they tested had traces of DNA from at least one Demodex species.
Anatomy of Mites
These mites are microscopic at around 0.3-0.4 mm 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.
But don’t rush off to scrub yourself down in boiling water quite yet; 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.
In order to collect mites for sampling, researchers usually press Scotch tape against a person’s skin and pull them out, pluck out hairs using tweezers, or scrape the skin and collect it for examination. This study, however, squeezed the skin on the nose to expel sebum from the pores, which was then scraped up. The sample was then transferred to a mineral oil until the DNA could be extracted.
The study found that 100% of samples from people over 18 yielded mite DNA, as did 70% of the teenagers that were studied. Why is this figure so different from previous studies that found whole mites less than a quarter of the time? Though each person has millions of hair follicles, the mites might not be evenly spread across the entire body. It’s very possible that the samples just aren’t taken in the right location. Additionally, the manner in which the mites are collected might not be reliable without more invasive methods.
Analyzing these mites at the genetic level could yield information about their diversity and offer clues as to where and when these mites first began hitching a ride on humans. The scientists hope to further their study by conducting similar research in different regions of the world in order to find out whether mites are ubiquitous there and, if so, how they might vary among geological regions.
Image credit: NCSU
[Hat tip: Wired]