A stye is caused by a bacterial infection in one of the tiny oil glands or hair follicles along your eyelid. The process almost always starts the same way: an oil gland gets clogged, its secretions stagnate, and bacteria (most commonly Staphylococcus aureus, a species that naturally lives on your skin) move in and trigger an infection. The result is a small, painful abscess on your eyelid that looks and feels like a pimple.
How the Infection Develops
Your eyelids contain dozens of tiny glands that produce oils to keep your eyes lubricated and your tears from evaporating too quickly. When those glands work normally, oil flows freely onto the surface of your eye every time you blink. Problems start when the opening of a gland gets blocked. The oil thickens, backs up, and creates a stagnant environment where bacteria can multiply rapidly. Your immune system responds by flooding the area with white blood cells, and the clash between bacteria and immune cells creates a pocket of pus and dead tissue.
This is, at its core, a tiny abscess. It forms quickly, often becoming noticeably red, swollen, and tender within a day or two.
External vs. Internal Styes
Not all styes form in the same place. External styes, which are far more common, develop at the base of an eyelash follicle or in one of the small oil glands (called glands of Zeis) near the lash line. You can usually see them clearly as a bump right at the edge of your eyelid.
Internal styes form deeper inside the eyelid, in the larger oil-producing glands called meibomian glands. These tend to be more painful because the swelling presses against the eye itself. They’re less visible from the outside, though you may notice a red, tender area when you flip the eyelid.
Risk Factors That Make Styes More Likely
Anything that increases the chances of clogged oil glands or introduces bacteria to your eyelids raises your risk.
- Blepharitis. This chronic inflammation of the eyelid margins is one of the strongest risk factors. It causes the oil glands to thicken and clog more easily, setting the stage for repeated infections.
- Touching or rubbing your eyes. Your hands carry bacteria. Rubbing your eyes transfers those bacteria directly to the gland openings along your lash line.
- Old or shared eye makeup. Mascara, eyeliner, and eyeshadow can harbor bacteria over time. Sharing these products spreads bacteria between people. Sleeping in eye makeup also blocks gland openings overnight.
- Contact lens handling. Inserting or removing lenses with unwashed hands introduces bacteria to the eye area. Lenses that aren’t properly cleaned can also carry organisms to the eyelid surface.
- Rosacea. People with rosacea, a condition that causes facial redness and skin inflammation, are more prone to eyelid problems. Research from the Rochester Epidemiology Project found that children who had styes were significantly more likely to develop rosacea as adults (5.5% compared to 1.5% of controls), suggesting a shared underlying tendency toward oil gland dysfunction.
- Previous styes. If you’ve had one, you’re more likely to get another. The same gland anatomy and skin bacteria that caused the first infection are still present.
How a Stye Differs From a Chalazion
People often confuse styes with chalazia (the plural of chalazion), and the two do look similar at first glance. The key difference is that a stye is an active bacterial infection, while a chalazion is a non-infectious inflammatory reaction. When a blocked meibomian gland leaks its oily contents into the surrounding tissue, the immune system treats that oil as a foreign substance and walls it off, creating a firm, painless nodule.
The easiest way to tell them apart: styes hurt. They’re tender to the touch, red, and often come to a visible head within a few days. Chalazia are typically painless lumps that develop more slowly. That said, a stye that doesn’t fully resolve can sometimes turn into a chalazion as the acute infection fades but the blocked gland remains inflamed.
What Happens as a Stye Heals
Most styes resolve on their own within one to two weeks. The abscess gradually comes to a head, drains (often while you sleep or during a warm compress), and the swelling subsides. Warm compresses are the most effective thing you can do to speed this along. Holding a clean, warm washcloth against the closed eyelid for 10 to 15 minutes several times a day softens the clogged oil, encourages drainage, and increases blood flow to the area.
Resist the urge to squeeze or pop a stye. Forcing it open can push the infection deeper into the eyelid tissue or spread bacteria to nearby glands. You should also avoid covering the area with makeup during the healing process, since cosmetics can further plug the gland and worsen the infection.
When a Stye Becomes Something More Serious
In rare cases, the infection can spread beyond the gland into the soft tissue around the eye, a condition called preseptal (periorbital) cellulitis. This causes diffuse redness and swelling across the entire eyelid rather than a localized bump. If that infection pushes deeper, past the thin membrane that separates your eyelid from your eye socket, it becomes orbital cellulitis, which is a medical emergency.
Warning signs that a stye has progressed include fever, pain that extends well beyond the bump itself, vision changes, swelling that spreads across the entire eyelid or to the other eye, and any bulging of the eyeball. These symptoms warrant immediate medical attention, particularly in children.
Preventing Recurrent Styes
Since the root cause is clogged oil glands plus bacteria, prevention targets both. Washing your hands before touching your face or handling contact lenses removes the most common bacterial source. Replacing eye makeup every three to six months and never sharing it limits bacterial buildup. Removing all eye makeup before bed keeps gland openings clear overnight.
If you have blepharitis or a tendency toward recurrent styes, a daily eyelid hygiene routine helps. This means gently cleaning your lash line with a warm washcloth or commercially available lid wipes to keep oil flowing and prevent the thickening and stagnation that starts the whole process. Warm compresses used regularly, even when you don’t have a stye, can keep meibomian glands from clogging in the first place.