Styes are caused by bacterial infection of the tiny oil glands along your eyelid margin. The bacterium responsible in most cases is Staphylococcus aureus, the same germ behind common staph infections. When debris, dead skin cells, or dried oil block one of these glands, bacteria that normally live on your skin get trapped inside, multiply, and form a small abscess filled with pus.
How a Stye Forms
Your eyelids contain dozens of small oil glands that continuously produce a thin layer of oil to protect and lubricate the surface of your eye. These oils drain through narrow ducts that open near your eyelash line. A stye develops when one of these ducts gets clogged, trapping oil inside the gland. Staph bacteria, which are already present on most people’s skin, colonize the stagnant oil. The resulting infection creates the painful, red, swollen bump you recognize as a stye.
On a cellular level, your immune system floods the infected gland with white blood cells, forming a pocket of pus and dead tissue. That’s what gives a stye its characteristic whitish or yellowish head after a day or two.
External vs. Internal Styes
Not all styes are the same. The type depends on which gland gets infected.
External styes are the most common. They form when bacteria infect the oil or sweat glands right at the base of your eyelashes. These tend to appear as a visible bump on the outer edge of the eyelid, and they typically come to a head within one to two days.
Internal styes develop deeper inside the eyelid, in glands called meibomian glands. You have roughly 30 to 40 of these glands in each eyelid, and they produce the oily component of your tear film. When one becomes infected, the swelling and pain are often more intense because the abscess sits beneath the eyelid’s surface rather than on it. Internal styes can sometimes progress into a chalazion, a firm, painless lump that forms when the infection clears but chronic inflammation remains in the blocked gland.
Common Triggers and Risk Factors
Anything that increases bacteria near your eyes or promotes gland blockage raises your stye risk. Several everyday habits are frequent culprits.
Touching your eyes with unwashed hands. Your fingertips carry staph bacteria. Rubbing your eyes transfers those bacteria directly to gland openings along your lash line.
Old or shared cosmetics. Eye makeup should be replaced every three to four months. Over time, bacteria colonize mascara wands, eyeliner pencils, and eyeshadow brushes. Sharing cosmetics with other people introduces additional bacteria through cross-contamination. Glitter or metallic makeup is particularly risky because flakes can fall into the eye and irritate gland openings. Experts also caution against using store testers that aren’t dispensed with single-use applicators, and against storing cosmetics above 85°F, which weakens preservatives designed to limit bacterial growth.
Contact lens hygiene. Handling lenses without washing your hands first, or wearing lenses longer than recommended, introduces bacteria to the eyelid area and can promote gland clogging.
Not removing makeup before bed. Leaving cosmetics on overnight traps debris around eyelash follicles, creating the exact conditions bacteria need to infect a blocked gland.
Skin Conditions That Increase Risk
Certain chronic conditions make styes more likely to occur, and to keep coming back.
Ocular rosacea is one of the most significant. This inflammatory condition affects the eyelids and the surface of the eye, and healthcare providers sometimes describe it as meibomian gland dysfunction because it directly impairs the oil glands in the eyelids. People with ocular rosacea often deal with recurrent styes, along with burning, redness, and a gritty sensation in the eyes.
Blepharitis, a condition marked by chronic inflammation of the eyelid margins, also increases the likelihood of styes. Crusting and bacterial overgrowth along the lash line create repeated opportunities for gland infection. Seborrheic dermatitis, the same condition that causes dandruff on the scalp, can produce similar flaking along the eyelids and contribute to blockages.
Does Stress Cause Styes?
No scientific studies have established a direct link between stress and styes. However, there are plausible indirect connections. Stress hormones can weaken the immune system, making it harder for your body to keep normal skin bacteria in check. Research has also found that stress hormones get converted into compounds that may help attract bacteria to vulnerable areas of the body. So while stress alone won’t cause a stye, it could tip the balance in favor of infection when other risk factors are already present.
Sleep deprivation follows a similar logic. Poor sleep suppresses immune function and may also lead people to rub their eyes more frequently, increasing the chance of transferring bacteria to eyelid glands.
Styes vs. Chalazia
People often confuse styes with chalazia because both produce a bump on the eyelid, but the causes differ. A stye is an active bacterial infection. It hurts, turns red, and may develop a visible pus-filled head. A chalazion, by contrast, is a chronic inflammatory reaction, not an active infection. It forms when a blocked meibomian gland becomes surrounded by granular scar-like tissue instead of healing normally. Chalazia are typically painless and firmer to the touch. They often develop from internal styes that didn’t fully resolve.
How Long Styes Last
Most styes resolve on their own within one to two weeks. A warm compress held against the closed eyelid for 10 to 15 minutes several times a day helps soften the blocked oil and encourages the stye to drain naturally. Resist the urge to squeeze or pop it, which can spread the infection deeper into the eyelid.
You should pay attention to how things progress in the first 48 hours of home care. Worsening pain or swelling after two to three days, pus or blood leaking from the bump, blisters forming on the eyelid, eyelids that feel hot to the touch, vision changes, or an eye that swells shut all warrant a visit to an eye care provider. Styes that keep recurring may signal an underlying condition like blepharitis or ocular rosacea that needs its own treatment.