Styes form when bacteria infect one of the tiny oil glands along your eyelid margin. In about 90% of cases, the culprit is Staphylococcus aureus, a common bacterium that already lives on your skin. When an oil gland gets blocked, bacteria multiply inside it, triggering the red, painful bump you recognize as a stye.
What Happens Inside the Eyelid
Your eyelids contain dozens of small glands that produce the oily layer of your tear film. Along the lash line, each eyelash has one or two tiny sebaceous glands that open directly into the hair follicle. These glands can become clogged with dead skin cells, dried oil, or debris. Once blocked, bacteria that normally sit harmlessly on the skin surface get trapped inside, multiply, and cause a localized infection. The result is a small, pus-filled bump that looks and feels a lot like a pimple.
There are two types. An external stye, the more common kind, develops at the base of an eyelash when the glands around the follicle become infected. It appears as a yellowish pustule right at the eyelid margin, surrounded by redness and swelling. An internal stye forms deeper in the eyelid when one of the larger oil glands embedded in the eyelid tissue gets infected. Internal styes tend to be more painful and can cause more intense swelling, sometimes accompanied by fever or chills. You might not see an obvious bump on the outside, but flipping the eyelid reveals a small raised yellow area on the inner surface.
Common Causes and Risk Factors
Anything that introduces bacteria to your eyelid or blocks those oil 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 direct route for transferring staph bacteria to your eyelid glands.
- Old or shared eye makeup. Bacteria grow easily in creamy or liquid cosmetics. The American Academy of Ophthalmology recommends replacing eye makeup every three months and never sharing it, even with family.
- Sleeping in contact lenses. Leaving lenses in overnight traps bacteria against the eyelid and reduces oxygen flow, creating conditions that favor infection.
- Not removing makeup before bed. Leftover mascara, eyeliner, and shadow can clog the gland openings along your lash line overnight.
Certain chronic conditions also make styes more likely to recur. Blepharitis, a persistent low-grade inflammation of the eyelid margins, keeps the oil glands irritated and prone to blockage. Ocular rosacea, which causes redness and swelling around the eyes, is closely linked to both styes and a related bump called a chalazion. If you get styes repeatedly, one of these underlying conditions may be the reason.
Are Styes Contagious?
Styes are not contagious. They are a localized infection of your own oil glands, not something you catch from another person. That said, the staph bacteria responsible are easily spread by hand contact. If you touch an active stye and then touch your other eye, you could potentially trigger a new one. Basic hygiene (washing your hands, not sharing towels or pillowcases) is enough to prevent spread.
What a Stye Feels Like
The first sign is usually tenderness or a gritty, foreign-body sensation along the eyelid. Within a day or two, a distinct bump forms. The area around it becomes red, swollen, and warm to the touch. Your eye may water more than usual, and bright light can feel uncomfortable. External styes are easy to spot as a visible bump at the lash line. Internal styes cause more diffuse swelling across the eyelid and may not show a clear bump from the outside.
How Long Styes Last
Most styes resolve on their own within one to two weeks. They typically come to a head, drain, and then heal without any treatment beyond basic home care. The standard approach is a warm compress: soak a clean washcloth in warm water, wring it out, and hold it gently against the closed eye for five minutes, several times a day. The warmth helps soften the blocked oil and encourages the stye to drain naturally. Resist the urge to squeeze or pop it, which can push the infection deeper into the eyelid tissue.
Signs of a Problem
Most styes are harmless, but a small number progress to more serious infections. Watch for swelling that gets worse after the first two to three days instead of better, pus or blood leaking from the bump, blisters forming on the eyelid, your eye swelling shut, or any change in your vision. Eyelids that feel hot to the touch are another warning sign. These symptoms can indicate the infection is spreading beyond the gland into the surrounding tissue, which needs medical treatment.
Styes that keep coming back, especially in the same spot, sometimes need to be drained by an eye doctor. Recurrent styes are also worth investigating for an underlying condition like blepharitis or rosacea that may need its own treatment to break the cycle.