A stye is caused by a bacterial infection in one of the small oil-producing glands along your eyelid margin. The bacterium responsible in most cases is Staphylococcus aureus, a common species that already lives on your skin. When one of the tiny gland openings near your eyelashes gets blocked, oil backs up behind the blockage, and bacteria that would normally be harmless multiply in that trapped fluid. The result is a red, tender bump that looks and feels a lot like a pimple.
How the Infection Starts
Your eyelids contain several types of glands that produce oils to keep your tear film stable and your lashes lubricated. When these glands are working normally, their secretions flow freely onto the surface of your eye. A stye forms when one of these gland openings becomes obstructed, usually by thickened oil, dead skin cells, or debris. Once the opening is plugged, the oily secretion stagnates behind it. That stagnant environment is where Staphylococcus aureus thrives, triggering the infection and swelling you see on the outside.
Other organisms that normally live on eyelid skin can sometimes play a role too, including tiny mites called Demodex that inhabit hair follicles. But staph bacteria remain the primary culprit in the vast majority of styes.
External vs. Internal Styes
Not all styes form in the same spot, and the location depends on which gland is affected. An external stye, the more common type, originates from a blockage in one of the small oil or sweat glands (called the glands of Zeis or Moll) that sit right at the base of your eyelashes. These tend to appear as a visible bump on the outer edge of your eyelid, close to the lash line.
An internal stye develops deeper inside the eyelid, in a larger oil gland called a meibomian gland. These glands are embedded in the firm tissue (tarsal plate) that gives your eyelid its shape. Because they’re farther from the surface, internal styes can feel more painful and may not be as easy to see. You might notice swelling and tenderness on the inner side of the lid rather than a clear bump on the outside.
What Makes Styes More Likely
Certain conditions make the glands in your eyelids more prone to blockage, which in turn raises your chances of getting a stye. The most significant is blepharitis, a chronic low-grade inflammation of the eyelid margins. Blepharitis thickens the oils your glands produce, making them more likely to clog. If you’ve had one stye, blepharitis is often the reason you keep getting more.
Ocular rosacea, a form of rosacea that affects the eyes, is another common contributor. It causes ongoing inflammation of the eyelids and is closely linked to meibomian gland dysfunction, the same process that sets the stage for internal styes. People with ocular rosacea frequently develop styes and chalazia as part of the condition’s pattern.
Everyday habits matter too. Touching your eyes with unwashed hands introduces extra bacteria to the eyelid margin. Sleeping in eye makeup or using old cosmetics can clog gland openings. Contact lens wearers who handle their lenses without washing their hands first also face a higher risk.
What a Stye Feels Like
A stye typically starts as a small area of tenderness along the eyelid, often with mild swelling and redness. Over a day or two, it develops into a well-defined, painful bump right at the lid margin. You may notice your eye watering more than usual, and the eyelid can feel heavy or gritty. Some people experience sensitivity to light. The bump often develops a visible white or yellowish point at its center as pus collects, similar to a pimple coming to a head.
How a Stye Differs From a Chalazion
A chalazion can look similar to a stye, but the two are different. A stye is an active infection: it’s painful, red, and sits right at the eyelid edge. A chalazion is a firm, usually painless lump that forms in the middle portion of the lid, farther from the lash line. It develops when a blocked meibomian gland becomes chronically inflamed without an active bacterial infection. Sometimes a stye that doesn’t fully drain will turn into a chalazion over time.
If the redness and swelling spread well beyond the bump and across the eyelid, or if your vision changes or it hurts to move your eye, that pattern is more consistent with a skin infection around the eye (preseptal cellulitis) and needs prompt medical attention.
How Long Styes Last
Most styes resolve on their own within one to two weeks. The bump gradually comes to a head, drains on its own, and the swelling subsides. You don’t need to squeeze or pop it. Forcing it open can push the infection deeper into the eyelid tissue and make things worse.
The single most effective thing you can do at home is apply a warm, moist compress to the affected eye for 5 to 10 minutes, 3 to 6 times a day. The warmth softens the hardened oil blocking the gland and encourages natural drainage. Use a clean washcloth soaked in warm (not hot) water. Don’t heat a wet cloth in the microwave, as it can become hot enough to burn the delicate eyelid skin. Re-wet the cloth as it cools to keep the temperature consistent throughout the compress.
When a Stye Needs Medical Treatment
If a stye is very painful or hasn’t started improving within about two days of consistent warm compresses, it’s worth having it evaluated. A doctor may prescribe antibiotic eye drops or a topical antibiotic cream to apply directly to the eyelid. If the infection persists or begins spreading beyond the eyelid itself, oral antibiotics may be necessary. In rare cases where a stye forms a large, contained pocket of pus that won’t drain on its own, a clinician can make a small incision to release it.
Styes that keep coming back are usually a sign of an underlying eyelid condition like blepharitis or meibomian gland dysfunction. Managing that root cause with daily lid hygiene, including warm compresses and gentle cleaning of the lash line, can break the cycle of recurrent infections.