A stye is caused by a bacterial infection in one of the tiny glands along your eyelid. The culprit is almost always Staphylococcus aureus, a common bacterium that lives on your skin and inside your nose. When this bacterium gets into an oil gland or hair follicle on your eyelid, it triggers a painful, red bump that looks similar to a pimple.
How the Infection Starts
Your eyelids contain dozens of small glands that produce oils to keep your eyes lubricated. When these glands become clogged, their secretions thicken and stagnate, creating the perfect environment for bacteria to multiply. The resulting infection is what forms the tender, swollen lump you recognize as a stye.
There are two types, depending on which gland gets infected. An external stye forms at the base of an eyelash, where a small oil gland opens into the hair follicle. These are the most common and appear right at the eyelid’s edge. An internal stye develops deeper inside the eyelid, in one of the larger oil-producing glands embedded in the eyelid tissue. Internal styes tend to point inward, sometimes visible as a yellowish spot on the inner surface of the lid.
Common Risk Factors
The bacterium that causes styes already lives on most people’s bodies. The problem isn’t the bacteria itself but how it reaches the eye. The most common route is simple: touching your nose, then rubbing your eye. S. aureus thrives in the nasal passages, so this everyday habit transfers bacteria directly to your eyelid glands.
Other behaviors that increase your risk include:
- Sleeping in old makeup: Cosmetics left on overnight can block gland openings and introduce bacteria. Sharing eye makeup with someone who has a stye can also spread the infection.
- Wearing contact lenses with unclean hands: Handling lenses without washing your hands first pushes bacteria toward the eyelid margin.
- Sharing pillowcases, washcloths, or towels: Styes are contagious, and bacteria transfer easily through fabrics that touch the face.
- Chronic eyelid inflammation (blepharitis): This condition causes ongoing irritation along the lash line, keeping glands partially blocked and primed for infection.
There’s also an interesting link to rosacea. A study using the Rochester Epidemiology Project found that children who had styes were more likely to develop rosacea as adults (5.5% compared to 1.5% in a control group). While 94.5% of children with styes never developed rosacea, the connection suggests that people prone to styes may share an underlying tendency toward certain inflammatory skin conditions.
Stye vs. Chalazion
Not every bump on your eyelid is a stye. A chalazion looks similar but develops differently and feels different. A stye is an active infection: it’s red, very painful, and tender to the touch from the start. It typically sits right at the eyelid’s edge. A chalazion, on the other hand, is a clogged oil gland that swells without necessarily being infected. It usually forms farther back on the eyelid, grows more slowly, and is painless at first. You might not even notice a chalazion until it’s large enough to feel with your finger.
The distinction matters because a chalazion can actually begin as an internal stye. If an infected gland doesn’t fully drain, the remaining blockage can harden into a chalazion that lingers for weeks or months.
What a Stye Feels Like
The first sign is usually tenderness and redness along the eyelid. Within a day or two, a distinct lump forms. Your eye may feel sore, scratchy, or watery. Some people notice their entire eyelid swelling, not just the bump itself. Most styes come to a head and drain on their own within several days, similar to how a skin blemish resolves.
Helping a Stye Heal
The most effective home treatment is a warm compress. Soak a clean washcloth in warm water, wring it out, and hold it against your closed eye for 5 to 10 minutes. Re-wet the cloth as it cools. After the compress, gently massage the eyelid to encourage the blocked gland to open and drain. Doing this two to three times a day can speed up resolution significantly.
Resist the urge to squeeze or pop a stye. Forcing it open can spread the infection to surrounding tissue. If you wear contact lenses, switch to glasses until the stye clears, since a lens can trap bacteria against the eye if the stye ruptures. Skip eye makeup during this time as well.
When a Stye Becomes Something More Serious
Most styes resolve without complications, but occasionally the infection spreads to the soft tissue surrounding the eye, a condition called preseptal cellulitis. Signs include widespread swelling, warmth, and redness across the eyelid and surrounding skin, sometimes with a fever. The eyelid may swell so much that it’s difficult to open. The key difference between a severe stye and preseptal cellulitis is scale: the swelling extends well beyond a single bump.
With preseptal cellulitis, vision and eye movement remain normal once the swollen lid is opened. That’s an important distinction from a deeper infection behind the eye, which can affect how the eye moves and sees. A stye that hasn’t improved after a week, keeps recurring, or produces spreading redness and fever warrants a visit to an eye specialist who can determine whether antibiotics or drainage are needed.