Thursday, September 6, 2012

Do fecal bacteria from face mites cause rosacea?

Image via Wikipedia. License
Back when I taught college general biology, I always gave a lecture in which we talked about ecosystems. At the beginning of the lecture, I showed them the above image or a similar one and explained that the handsome organism it features lives quietly and unobtrusively in the hair follicles on your face. My goal was to combine horror and information so that my students would never forget that they, too, are ecosystems--and, I hoped--get acclimated to the idea. Most of them just seemed pretty creeped out.

The animal above is a mite and member of the Demodex genus. Because of its affinity for follicles, it's known as Demodex folliculorum. Its partner in existence on your face (and some other places) is the shorter version, known as Demodex brevis [PDF], which is drawn to your sebaceous (oil) glands, also on your face. Because they have "piercing-sucking mouth parts," pedipalps, and eight legs in four pairs, according to one lovingly detailed description in a 1976 paper, they are arachnids, just like spiders. Tiny arachnids that live on your face, taking moonlit strolls when it's dark and diving for cover in light. They live there, just as you live in a house, except your face is like an array of microscopic cave houses where these organisms reproduce and eat. And apparently are rather active; from a 1985 paper about these mites and what they do on your eyelids:
The normally torpid existence of demodectic mites of the eyelid changes with the onset of oviposition (egg laying). There occurs a burst of activity characterized by flexion, extension, and rotation.
In addition to all of flexing and extending and rotating, these mites also happen to die on your face. They "disgorge" products from their salivary glands while alive, but when dead, they appear to disintegrate, releasing the contents of their guts onto you and the visage you show the world. As it happens, the mites themselves are, like you, hosts to unseen organisms, in this case the bacteria in their guts.

The word on the street--and in this paywalled paper--is that these mites don't have anuses. Thus, after suffering from a near-lifelong (a few days at most) case of constipation, they die and unconstipate all over you. 

If the idea of dead mites reproducing and dying and disintegrating all over your face didn't do you in, congratulations. You're a rational person resigned to your inevitable fate as an ecosystem. Either way, you may have wondered: What does this mite-y fecal matter do to my face?

Experts have disagreed about what these mites and their, er, exudants do to their host, but studies have found links between their presence and abundance and several dermatological and other diseases. Among these, rosacea is possibly the best known, in part because it is relatively common (up to 3% of people worldwide have it) and easy to spot: It produces a pronounced redness of the skin, sometimes with a sandpapery look, and with age and as it worsens, can result in manifestations like bumps on the skin and gritty eyes, including effects on the nose like those in this painting:
A nose with features of end-stage rosacea (left).
Public domain, via Wikimedia Commons.
Indeed, as we age, the population of these mites grows, and rosacea is considered a chronic condition that crops up most often between the ages of 30 and 50 or 60. It also has had an air of mystery about it, including why some people develop it and others do not, and what, exactly, causes it. Now, researchers who have conducted a deep review of all of the rosacea-related research suggest that it's primarily a bacterial infection. The source of the bacteria? That mite poop. 

Does that mean that people who don't have rosacea are in some way less fecally affected than people who do? Not necessarily. These mites are "commonly" found on people without any outward manifestation of effect. But people with rosacea may develop it thanks to wonky immune systems that underreact or overreact to the mites or the bacteria in their poop, according to the authors of the review, published in the Journal of Medical Microbiology. 

In other words, people who have rosacea might actually be fighting the mites and their poop contents harder than people without it, so no need to feel all superior if you're rosacea free. Rosacea is more common in women than in men, which is in keeping with a general female prevalence of disorders of immune wonkiness. Also, just in case menopause didn't carry enough baggage, rosacea happens to strike women "particularly" during that time our ovaries are saying their sayonaras.

One of the bacteria in question actually might begin as just another resident lurking in the ecosystem that is your skin. The mites eat the bacteria along with the delicious (I'm assuming) skin cells they consume. When the mites die and disintegrate, bacterial bits may emerge along with other components of the mite digestive contents. It is possible, say the review authors, that these bacterial bits--like lots of other bacterial bits--trigger an immune response that we see as rosacea. Indeed, one antibiotic, doxycycline, that's particularly well known for conquering this bacterium, is reasonably effective for rosacea.

What can you or any of us do to prevent or treat rosacea? As far as prevention, the review authors note that in some cases, a genetic immune wonkiness may predispose some people to developing it. Because these mites often are deeper than skin surface, techniques like exfoliation are unlikely to be helpful. As science writer Ed Yong cautions in his fantastic piece about this review paper, do not try to bleach your face, either. Current treatment consists of a topical medication to reduce inflammation and oral antibiotics. In severe cases, a medication used for cystic acne and that actually inhibits sebaceous gland secretion is a possibility.

Do you or does someone you know have rosacea? What treatments have you tried? Given the potential involvement of a wonky immune system, have you noted any co-occurrence of other immune-related problems?


  1. Great article. Like you I have used this imagery and idea to start a presentation on humans as part of an ecosystem. Similarly the idea just seems to gross people out. I combine it with the 10:1 bacteria v human cells, and 2kg of their body is not human and their horror is complete. One of my favourite images is at