Demodex mites eat sebum (the oily substance your skin produces), skin cells, and even bacteria living inside your hair follicles. These microscopic mites live on nearly every adult’s face, feeding on the natural oils and cellular debris that accumulate in pores and along eyelash roots. The two species that live on humans have slightly different dietary preferences, and the way they feed can, in some people, trigger skin and eye problems.
The Two Species Eat Different Things
Two species of demodex live on human skin, and they’ve carved out separate niches based on what they consume. Demodex folliculorum tends to live in smaller hair follicles, especially eyelash follicles, where it primarily eats skin cells. Demodex brevis prefers the oil glands connected to hair follicles, where it feeds mainly on sebum. Both species have pin-like mouthparts designed to pierce and consume what they find inside the follicle, including hormones that accumulate there alongside oils and dead cells.
This division of territory means the two species aren’t really competing with each other. Folliculorum clusters around lash roots and follicle openings, sometimes in groups. Brevis is more solitary and burrows deeper into sebaceous glands. Their different diets explain why they show up in different locations on your face, with folliculorum more common on eyelids and brevis more common in oilier areas like the nose and cheeks.
How They Digest Their Food
Demodex mites don’t simply bite and swallow. They secrete digestive enzymes directly onto nearby tissue, breaking down skin cells externally before consuming them. These enzymes, primarily lipases (which break down fats) and proteases (which break down proteins), dissolve the cell walls of epithelial tissue and liquefy the oily contents of sebaceous glands. The mites then ingest the pre-digested material through their needle-like mouthparts.
This external digestion process is important because it’s also the main way demodex mites cause problems. The enzymes they deposit don’t just dissolve their food. They sit on the surrounding skin tissue and can cause direct irritation. The mites also digest bacteria and other microorganisms living in the follicle, using the same lipase enzymes that break down sebum. So while bacteria aren’t their primary food source, mites do consume them as part of their feeding process.
Why Feeding Happens Mostly at Night
Demodex mites are nocturnal. They travel across the skin’s surface at speeds of 8 to 16 millimeters per hour, but only in the dark. Bright light sends them retreating back into follicles. This means their active feeding and movement peaks while you sleep. During the day, they stay anchored deep inside follicles using tiny scales that cover their bodies, quietly digesting sebum and skin cells in place.
What Mites Leave Behind
The real issue with demodex feeding isn’t what goes in. It’s what comes out. As mites consume epithelial cells, their sharp claws create tiny abrasions along the follicle wall. They deposit waste material consisting of digestive enzymes, partially digested skin cells, keratin fragments, and eggs directly onto human tissue. The lipases and proteases in this debris can trigger a type 1 allergic response, causing surface irritation and inflammation.
Demodex mites also carry bacteria on their surface and inside their bodies. Species like Staphylococcus, Streptococcus, and notably Bacillus oleronius travel with the mites and produce antigens that provoke an immune response. When mite populations grow large enough, this combination of digestive waste, bacterial antigens, and physical damage to follicle walls can overwhelm local immune tolerance and trigger visible skin disease.
When Feeding Causes Skin Problems
Most people carry demodex mites without any symptoms. A density of more than 5 mites per square centimeter of skin is the threshold doctors use to diagnose demodicosis, a condition where mite populations have grown large enough to cause problems. Below that number, the feeding activity is too minor to notice.
In rosacea, the relationship between mites and skin becomes a feedback loop. Mite feeding triggers inflammation, which alters the local skin environment in ways that actually support more mite growth, which causes more inflammation. The pro-inflammatory signals released in response to mite debris and bacterial antigens include molecules that break down the skin’s protective barrier, making the cycle harder to interrupt on its own.
On the eyelids, demodex feeding is linked to blepharitis, a chronic inflammation of the eyelid margin. As mites feed on cells around lash roots, the accumulated debris, including decomposing mite remains and their chitinous exoskeletons, can physically block the tiny oil glands (meibomian glands) that keep your tear film stable. Over time, this blockage may lead to permanent changes in gland structure and chronic dry eye symptoms.
Who Has the Most Mites Feeding on Them
Demodex populations grow throughout your life as your skin produces more oil. Only about 13% of children aged 3 to 15 carry detectable mites. By the late teens and early twenties, that number rises to roughly 34%. The real jump comes later: 84% of people over 60 carry demodex, and by age 70, the rate hits 100%. Every person over 70 who has been tested in studies has had mites feeding on their skin.
This age pattern makes sense given what the mites eat. Children produce less sebum, so there’s less food available. Sebum production peaks in adolescence and remains steady through adulthood, giving mite populations decades to slowly build. The mites reproduce entirely within hair follicles, so once they’re established, the constant supply of oil and dead skin cells sustains a growing colony for life.