Styes form when bacteria infect one of the tiny oil or sweat glands along your eyelid margin. The culprit is almost always Staphylococcus aureus, a common bacterium that many people carry on their skin and inside their nose without any problems. The infection starts when that bacterium finds its way into a blocked or vulnerable gland, triggering a painful, red bump that looks a lot like a pimple.
How the Infection Starts
Your eyelids contain dozens of small glands that produce oils and moisture to keep your eyes lubricated. When one of those glands gets clogged with dead skin cells, dried oil, or debris, bacteria that are already living on your skin can multiply inside the blocked gland. The result is a localized infection: swelling, redness, and a tender bump that fills with pus.
The most common way the bacteria reach your eyelid is simple. You touch your nose, where staph bacteria often live harmlessly, and then rub your eye. That transfer is enough to seed an infection if a gland happens to be blocked or irritated. You don’t need exposure to anything unusual. The bacteria are already on you.
External vs. Internal Styes
Not all styes form in the same spot. External styes develop at the base of an eyelash, in the small oil or sweat glands (called Zeis and Moll glands) right along the lash line. These are the ones you can typically see as a yellowish bump on the outer edge of your eyelid.
Internal styes form deeper inside the eyelid, in the larger oil-producing glands embedded in the eyelid’s firm inner plate. These tend to be more painful because the swelling pushes against the eye itself, and they’re harder to see without flipping the eyelid. Both types are caused by the same bacterial process, but internal styes can take longer to resolve because drainage is more difficult.
Common Risk Factors
Certain habits make styes more likely by introducing bacteria to your eyelids or clogging the glands that line them:
- Rubbing your eyes. This irritates the delicate eyelid tissue and pushes bacteria from your fingers directly into the glands.
- Sleeping in makeup. Mascara and eyeliner can block gland openings overnight, creating the perfect environment for bacterial growth. Old makeup is especially risky. Replace mascara at least every six months, because bacteria accumulate in the tube over time.
- Dirty or expired contact lenses. Handling lenses with unwashed hands or wearing them longer than recommended increases bacterial exposure.
- Previous styes. If you’ve had one before, you’re more likely to get another because the underlying gland blockage or bacterial colonization tends to recur.
People with chronic eyelid inflammation, a condition called blepharitis, are particularly prone to styes because their eyelid glands are already irritated and partially blocked much of the time.
Are Styes Contagious?
Technically, yes, but barely. The staph bacteria that cause styes can be transferred through direct contact or shared items like towels and pillowcases, but this rarely leads to another person developing a stye. Most people already carry the same bacteria on their skin. That said, it’s reasonable not to share face towels or pillowcases with someone who has an active stye, and to wash your hands after touching your own infected eyelid to avoid spreading it to your other eye.
How Long Styes Last
Most styes resolve on their own within one to two weeks. In the first day or two, the bump becomes tender and swollen, then gradually forms a visible head of pus. Eventually the stye drains, the swelling goes down, and the eyelid returns to normal. Applying a warm, damp washcloth to the closed eyelid for 10 to 15 minutes, two to three times a day, helps soften the blocked gland and encourages it to drain naturally. Gently washing the affected eyelid with mild soap and water can also speed the process along.
Resist the urge to squeeze or pop a stye. Forcing it open can push the infection deeper into the eyelid tissue and make things significantly worse.
Styes vs. Chalazia
A chalazion can look like a stye at first, with the same redness and swelling, but the two diverge quickly. After a day or two, a stye stays painful and stays anchored to the eyelid margin, right along the lash line. A chalazion migrates toward the center of the eyelid and becomes a firm, painless nodule. Chalazia are caused by a blocked oil gland without active bacterial infection, so they’re more of an inflammatory lump than an infected one. They can linger for weeks or months and sometimes need a minor in-office procedure to drain, whereas most styes clear up on their own.
When a Stye Becomes Serious
Styes are usually harmless, but in rare cases the infection can spread from the gland into the surrounding eyelid tissue. This is called preseptal cellulitis, and it turns the entire eyelid red, swollen, and warm to the touch rather than producing a single localized bump. If the infection pushes even deeper, past the tissue barrier that separates the eyelid from the eye socket, it becomes orbital cellulitis, which is a medical emergency.
Signs that an infection has moved beyond a simple stye include fever, pain that spreads across the entire eye area, changes in vision, and any bulging of the eye itself. These symptoms warrant an immediate trip to the emergency room, especially in children, who are more susceptible to these complications.
Preventing Styes
The most effective prevention is keeping bacteria away from your eyelid glands. Wash your hands before touching your face or handling contact lenses. Remove all eye makeup before bed, and throw out mascara and liquid eyeliner that’s more than six months old. If you’re prone to recurring styes, a daily eyelid scrub with a small amount of baby shampoo diluted in warm water helps keep the glands clear and reduces the bacterial load along your lash line.
Warm compresses aren’t just for treating styes. Using them a few times a week can keep the oil in your eyelid glands flowing freely, which reduces the blockages that give bacteria a foothold in the first place.