Blepharitis develops when the eyelid margins become chronically inflamed, and it happens through several distinct pathways depending on which part of the eyelid is affected. Roughly 58% of patients seen in U.S. eye care clinics show signs of at least one form of it, making it one of the most common eye conditions. There isn’t a single cause. Instead, blepharitis results from an interplay of bacteria, skin conditions, microscopic mites, and gland malfunction.
Anterior vs. Posterior: Two Different Problems
The eyelid margin has two zones, and inflammation in each one has different triggers. Anterior blepharitis affects the skin of the eyelid, the base of the eyelashes, and the hair follicles. Posterior blepharitis affects the tiny oil glands (meibomian glands) embedded deeper in the eyelid. Both types frequently overlap, and many people have both at the same time.
Bacterial Overgrowth on the Lid Margin
Staphylococcus bacteria are the classic culprit behind anterior blepharitis. These bacteria naturally live on skin, but when they overpopulate along the eyelid margin, their byproducts irritate the surrounding tissue. The exact mechanism isn’t fully settled. Bacterial toxins may directly irritate the lid, or the immune system may overreact to the bacteria’s presence, or both. The result is redness, crusting at the lash line, and a gritty, burning sensation.
A related form, seborrheic blepharitis, involves less outright inflammation but produces oily, greasy flakes along the lash line. It’s closely tied to seborrheic dermatitis, the same condition that causes dandruff on the scalp and eyebrows. If you have dandruff, you’re more likely to develop this type of eyelid inflammation.
Eyelash Mites and Collarettes
Tiny mites called Demodex live in most people’s eyelash follicles without causing problems. When their population grows too large, though, they trigger a specific pattern of blepharitis. The mites act as mechanical carriers of bacteria, physically transporting organisms like Staphylococcus and Streptococcus into the follicle and onto the lid surface. Even after the mites die, the bacteria they’ve introduced can continue fueling inflammation.
The hallmark sign is collarettes: waxy, cylindrical deposits that wrap around the base of each eyelash like a plug. These are composed of undigested material, skin cells, keratin, and mite eggs. They look distinctly different from the loose, flaky scales of seborrheic blepharitis. When an eye doctor pulls off a collarette, the tails of Demodex mites are often visible protruding from the follicle under magnification. One large study of over 1,000 consecutive patients found that 58% had collarettes, suggesting Demodex blepharitis affects an estimated 25 million eye care patients in the U.S.
Symptoms of Demodex blepharitis include itching, burning, dryness, irritation, watery eyes, blurry vision, and a sensation of heavy eyelids.
Meibomian Gland Dysfunction
Posterior blepharitis most often stems from a problem with the meibomian glands, which produce the oily layer of your tear film. That oil slows tear evaporation and keeps the eye’s surface smooth. When these glands malfunction, the process follows a predictable cycle.
First, the oil inside the glands stagnates instead of flowing freely onto the tear film. That stagnant oil creates a breeding ground for bacteria and mites. The bacteria then release enzymes that break down the oil’s fats, making the secretion thicker and raising its melting temperature. Thicker oil is harder to squeeze out of the gland opening, which causes more stagnation, more bacterial growth, and more inflammation. The cycle is self-reinforcing: once it starts, it tends to persist unless something interrupts it.
The altered oil also changes the composition of the tear film itself. Whether the glands produce too little oil or oil with an abnormal chemical makeup, the result is the same: the tear film becomes unstable, the eye surface dries out faster, and irritation follows. This is why blepharitis and dry eye disease so frequently occur together.
Skin Conditions That Drive Eyelid Inflammation
Rosacea, a chronic inflammatory skin condition that causes facial redness and visible blood vessels, is one of the strongest drivers of blepharitis. Studies estimate that 6 to 58% of rosacea patients develop eye involvement. The ocular form of rosacea triggers an overactive inflammatory and immune response in the skin, which ramps up production of proteins that promote blood vessel growth and tissue irritation. Elevated levels of inflammatory molecules in tear fluid add to the problem. The hallmarks of ocular rosacea are bilateral chronic blepharitis, meibomian gland dysfunction, and visible tiny blood vessels along the lid margin.
Seborrheic dermatitis is the other major skin condition linked to blepharitis. The same process that produces oily, flaking skin on the scalp, eyebrows, and sides of the nose extends to the eyelids in many people.
Allergies, Cosmetics, and Contact Lenses
Allergic reactions can trigger or worsen eyelid inflammation. Common offenders include eye makeup, contact lens solutions, and prescription eye drops. The allergic response itself inflames the lid margin, and products that aren’t fully removed at the end of the day provide additional material for bacteria to feed on.
Contact lens wear doesn’t directly cause blepharitis, but it can complicate it. Lenses sit on the tear film, so when the tear film is already unstable from meibomian gland problems, contacts become less comfortable and may worsen irritation. Some people with blepharitis can still wear contacts with proper treatment, but it depends on severity.
Age, Sex, and Other Risk Factors
Blepharitis occurs at all ages and across all racial groups, but some people are more vulnerable. In a population-based study of adults over 60, the prevalence of anterior blepharitis increased significantly after age 80. Male sex had the strongest association with developing the condition in that study. Lower education level, which often correlates with less access to eye care and different hygiene routines, was also a risk factor.
Dry eyes on their own raise the risk, since an unstable tear film creates conditions that favor bacterial overgrowth and gland obstruction. Having lice on the scalp or skin is another, less common cause of anterior blepharitis.
Why It Tends to Be Chronic
Most people who develop blepharitis find that it comes and goes rather than appearing once and resolving. This is partly because the underlying causes (skin conditions, mite populations, gland dysfunction) are themselves chronic. The self-reinforcing cycle of meibomian gland obstruction is a key reason posterior blepharitis persists: thickened oil leads to bacterial growth, which thickens the oil further. And Demodex mites reproduce in the follicles continuously, so without ongoing management, their numbers rebound. Understanding which type you have, and which of these mechanisms is driving it, is the starting point for breaking the cycle.