A stye is caused by a bacterial infection in one of the small oil or sweat glands along your eyelid margin. The bacterium most often responsible is Staphylococcus aureus, a common skin bacterium that normally lives on your face without causing problems. When it gets trapped inside a blocked gland, it multiplies, triggers inflammation, and produces the painful, red bump you see or feel on your eyelid.
How a Stye Forms
Your eyelids contain dozens of tiny glands that produce oils and moisture to protect the surface of your eye. When one of these glands becomes clogged, bacteria that are already present on your skin can get sealed inside. Cut off from the surface, the bacteria multiply in the trapped oil, and your immune system responds with inflammation. The result is a localized pocket of infection: swelling, redness, tenderness, and often a visible white or yellow head of pus.
Most styes point and drain on their own within one to two weeks. Once the pus drains, the pain resolves quickly and the bump shrinks over the following days.
External vs. Internal Styes
Where the stye appears depends on which gland is infected. An external stye forms on the outer edge of the eyelid, right at the base of an eyelash. It looks and behaves like a small pimple. It develops when bacteria infect one of the oil glands (glands of Zeis) or sweat glands (glands of Moll) that sit alongside your lash follicles.
An internal stye develops on the inner surface of the eyelid, facing your eyeball. These form when a meibomian gland becomes infected. Meibomian glands are larger oil glands embedded deeper in the eyelid tissue. Because of their location, internal styes tend to be more painful and less visible from the outside. You might notice a general swelling of the lid rather than a distinct bump. Internal styes can also take longer to resolve and are more likely to need medical treatment.
Common Triggers and Risk Factors
Anything that introduces bacteria to your eyelid margin or blocks those tiny glands raises your risk. The most common triggers are everyday habits you might not think twice about.
- Touching your eyes with unwashed hands. This is the single most common way bacteria reach your eyelid glands. Every time you rub your eyes, you transfer skin bacteria directly to the lash line.
- Old or shared eye makeup. Moisture in products like mascara and liquid eyeliner helps bacteria and mold grow faster over time. Each time you touch the applicator to your eye and then dip it back in the tube, you add bacteria to the product. Expired cosmetics can harbor enough bacteria to cause infections.
- Sleeping in makeup. Leaving eye makeup on overnight gives cosmetic residue hours to settle into gland openings and block them.
- Dirty or expired contact lenses. Handling lenses without washing your hands first, or wearing them past their replacement schedule, introduces bacteria directly to the eye area.
Chronic Conditions That Cause Recurring Styes
If you get styes repeatedly, the cause is often an underlying condition rather than a one-time hygiene lapse.
Blepharitis, a chronic inflammation of the eyelid margins, is one of the most common culprits. It creates a cycle: inflamed lids produce abnormal oil secretions, which clog glands, which become breeding grounds for bacteria. Blepharitis itself is also a risk factor for meibomian gland dysfunction, a condition where those deeper oil glands stop working properly. Meibomian gland dysfunction can cause chronic styes and recurring blockages in the tear system.
Ocular rosacea, a form of the skin condition rosacea that affects the eyes, causes similar gland inflammation and is strongly linked to repeated styes. People with diabetes are also more susceptible to bacterial infections generally, including styes, boils, and follicle infections. If styes keep coming back despite good hygiene habits, one of these conditions may be the underlying driver.
Stye vs. Chalazion
A chalazion looks similar to a stye but has a different cause. While a stye is an active bacterial infection, a chalazion is a blocked gland that has become inflamed without infection. A chalazion typically develops more slowly, hurts less, and feels like a firm, round lump rather than a tender, red bump. Sometimes a stye that doesn’t fully drain turns into a chalazion as the trapped material hardens.
The practical difference matters because they respond to different approaches. A stye is fighting an infection and usually resolves as pus drains. A chalazion is dealing with a non-infectious blockage and can persist for a month or longer before it needs professional attention.
What Happens as a Stye Heals
Most styes follow a predictable course. Within the first day or two, you’ll notice tenderness, swelling, and redness at the lid margin. Over the next two to four days, the infection comes to a head and the bump fills with pus. It then ruptures on its own, draining the material and relieving the pain. The whole process from first twinge to resolution usually takes one to two weeks.
Warm compresses speed this along. Soaking a clean cloth in warm water, wringing it out, and holding it gently over your closed eyelid for about three minutes helps soften the blocked oil and encourages the stye to drain. You may need to re-soak the cloth partway through to maintain the warmth. Doing this twice a day is the standard recommendation.
One important rule: don’t squeeze or pop a stye. Forcing it open can push the infection deeper into the eyelid tissue or spread bacteria to surrounding glands.
When a Stye Needs Medical Attention
Most styes are harmless and self-limiting, but a few warning signs call for professional evaluation. If the swelling spreads beyond the eyelid to the skin around your eye or cheek, that could indicate a secondary infection of the surrounding tissue. Any change in your vision alongside a stye is a red flag. And if a stye hasn’t started improving after a week of warm compresses, it likely needs more than home care.
For styes that don’t drain on their own, a doctor can make a small incision to release the trapped material. In cases where infection spreads to surrounding tissues, oral antibiotics are sometimes necessary. Internal styes are more likely to need this kind of intervention than external ones.
Preventing Styes
Prevention comes down to keeping your eyelid glands clean and unblocked. Washing your hands before touching your face or handling contact lenses is the simplest and most effective step. Replace mascara and liquid eyeliner every three months, and never share eye makeup with others. Remove all eye makeup before bed.
If you’re prone to styes or have been diagnosed with blepharitis, a daily lid hygiene routine helps keep glands clear. The goal is to remove crust, flakes, and excess oil from the lid margin. This involves a warm compress held over closed eyes for three minutes, followed by gentle cleaning of the lash line with a clean cloth or cotton swab. Doing this twice a day, with clean hands, reduces the buildup that leads to blockages. Over time, consistent lid hygiene can break the cycle of recurring infections.