A stye is caused by a bacterial infection in the eyelid, almost always from Staphylococcus aureus, a common bacterium that lives on your skin. When this bacterium gets into an oil gland or hair follicle along your eyelash line, it triggers a painful, red bump that looks similar to a pimple. Styes typically resolve on their own within one to two weeks, but understanding what causes them can help you avoid getting them repeatedly.
How a Stye Forms
Your eyelids contain dozens of tiny oil glands that help lubricate your eyes and keep tears from evaporating too quickly. They also have hair follicles at the base of every eyelash. A stye develops when bacteria enter one of these structures and multiply, creating a localized infection.
There are two types. An external stye forms at the base of an eyelash follicle, right along the edge of your lid. It’s the more common type, and it’s the one most people picture: a red, swollen spot that looks like a small boil. An internal stye forms deeper in the eyelid, inside one of the oil-producing glands (called meibomian glands). Internal styes tend to be more painful because the infection is trapped under the skin rather than coming to a head on the surface.
In both cases, the underlying process is the same. Bacteria get where they shouldn’t be, the gland or follicle becomes blocked and inflamed, and pus builds up. You’ll often notice a small white or yellow spot at the center of the bump as the infection comes to a head.
Common Triggers and Risk Factors
The bacteria responsible for styes already live on most people’s skin without causing problems. What tips the balance is usually a combination of blocked glands and bacterial transfer. Here are the most common triggers:
- Touching your eyes with unwashed hands. This is the single most common way bacteria reach your eyelids. Rubbing your eyes, adjusting contact lenses, or even resting your face in your hands throughout the day can introduce staph bacteria directly to vulnerable glands.
- Old or shared eye makeup. Infection-causing bacteria grow easily in creamy or liquid eye cosmetics. The American Academy of Ophthalmology recommends throwing away eye makeup after three months and never sharing it, even with close family. If you develop any eye infection, toss all your eye makeup immediately.
- Contact lens habits. Wearing contacts isn’t a direct cause, but poor lens hygiene increases your risk. Lenses can trap bacteria near the eye, and handling them with less-than-clean hands transfers bacteria to the eyelid with every insertion and removal. Using old solution, sleeping in lenses, or wearing them past their replacement schedule all contribute.
- Blepharitis. This is chronic inflammation of the eyelid margins that causes flaking, crusting, and irritation along the lash line. It creates an environment where oil glands clog more easily and bacteria thrive. People with blepharitis get styes far more often than people without it.
- Leaving makeup on overnight. Residual makeup can block oil gland openings and trap bacteria against the lid. Cleaning the base of your eyelashes with a cotton swab helps remove remnants that regular face washing can miss.
Conditions That Make Styes Recurrent
If you keep getting styes, there’s often an underlying condition at play. Ocular rosacea, a form of rosacea that affects the eyes, is one of the more common culprits. It causes chronic eyelid inflammation and is specifically associated with recurrent styes and other eyelid infections. Many people with ocular rosacea don’t realize they have it because their skin symptoms are mild or absent.
Meibomian gland dysfunction is another frequent cause of repeat styes. The oil glands in your eyelids produce secretions that become thickened and stagnant, plugging the gland openings. Once a gland is blocked, bacteria that would normally be harmless can multiply in the trapped oil and trigger an infection. This thickening and stasis of gland secretions is a well-documented precursor to both styes and chalazia.
Stye vs. Chalazion
People often confuse styes with chalazia (the plural of chalazion), and the two are related but distinct. A stye is an active bacterial infection. It’s very painful, appears right at the eyelid’s edge near the lashes, and can make the entire eyelid swell. You’ll often see a pus spot at the center.
A chalazion is a blocked oil gland without an active infection. It forms farther back on the eyelid, is usually painless or only mildly tender, and grows more slowly. Chalazia can actually start as internal styes: the infection resolves, but the gland remains clogged, leaving a firm bump. If you have a painless lump on your eyelid that’s been there for weeks, it’s more likely a chalazion than a stye. Chalazia can cause blurry vision if they grow large enough to press on the eyeball, which styes rarely do.
What a Stye Feels Like
The first sign is usually tenderness or a gritty, scratchy sensation in one spot on your eyelid, as if something is stuck in your eye. Within a day or so, a red, swollen bump appears. Common symptoms include a painful red lump at the lash line, a visible pus spot at the center of the bump, sensitivity to light, tearing in the affected eye, and crustiness along the eyelid margin when you wake up.
Most styes peak in pain and swelling within the first two to three days, then gradually improve as they drain. The whole process from first twinge to full resolution typically takes one to two weeks. If the pain and swelling haven’t started improving within 48 hours of home care (warm compresses applied for 10 to 15 minutes several times a day), or if they’re actually getting worse after the first two to three days, that’s a sign the infection may need professional treatment.
Preventing Styes
Since the root cause is bacteria reaching a vulnerable gland, prevention comes down to keeping bacteria away from your eyelids and keeping those glands flowing freely.
Wash your hands before touching your face or eyes, and especially before handling contact lenses. Replace contact lenses on the schedule your eye care provider recommends, use fresh solution every time (never top off old solution), and replace your lens case regularly. If you develop a stye while wearing contacts, discard the pair you were wearing when it appeared. The lenses may harbor the bacteria that caused the infection.
For makeup, replace mascara, eyeliner, and eyeshadow every three months. Avoid store testers that have been used by other people. At the end of the day, remove all eye makeup thoroughly, paying attention to the lash line where residue tends to collect.
If you have blepharitis or rosacea, managing those conditions with daily lid hygiene (warm compresses and gentle lid scrubs) reduces stye frequency significantly. Keeping the oil glands from clogging in the first place eliminates the environment bacteria need to cause trouble.