A stye is caused by a bacterial infection in one of the tiny oil or sweat glands along your eyelid margin. The bacterium responsible in roughly 90 to 95 percent of cases is Staphylococcus aureus, the same common skin bacterium behind many minor skin infections. It gets trapped in a gland, multiplies, and triggers the red, painful bump you see at the lash line or on the inner eyelid.
How the Infection Starts
Your eyelids contain dozens of small glands that produce oils and moisture to protect the surface of your eye. Along the lash line, oil glands and sweat glands open near the base of each eyelash. Deeper inside the eyelid, larger oil glands line the inner surface. When any of these glands becomes blocked, bacteria already living on your skin can get trapped inside, multiply, and cause a localized infection.
This is why styes come in two forms. An external stye develops when the small oil or sweat glands near the eyelash roots become blocked and infected. You’ll typically see a small yellowish pustule right at the base of a lash, surrounded by redness and swelling. An internal stye forms deeper in the eyelid, in the larger oil glands embedded in the eyelid’s firm inner plate. Internal styes tend to be more painful and point inward toward the eye rather than outward.
Risk Factors That Make Styes More Likely
Styes aren’t random. Certain habits and conditions make the glands in your eyelids more prone to blockage or more exposed to bacteria.
Touching Your Eyes
The simplest and most common trigger is transferring bacteria from your hands to your eyelids. Rubbing your eyes, adjusting contact lenses with unwashed hands, or even resting your face in your palms throughout the day can introduce bacteria directly into gland openings along the lash line.
Old or Shared Eye Makeup
Mascara, eyeliner, and eyeshadow applicators collect bacteria every time they touch your skin. The FDA notes that because of repeated microbial exposure during use, some industry experts recommend replacing mascara every three months. Adding water or saliva to dried-out mascara is especially risky because it introduces new bacteria directly into the tube. Sharing eye makeup with others spreads bacteria between people whose skin may carry different strains.
Contact Lens Habits
Contact lenses sit directly on the eye and can trap microbes against the surface. The American Academy of Ophthalmology identifies several lens habits that raise infection risk: sleeping in your lenses, using extended-wear lenses longer than recommended, reusing or topping off old contact lens solution instead of replacing it fresh, and not rubbing your lenses during cleaning (even if the solution label says “no rub”). Each of these allows bacteria to build up on or under the lens, where they can easily reach the eyelid glands.
Chronic Eyelid Inflammation
Blepharitis, a condition where the eyelid margins stay chronically inflamed, is one of the strongest risk factors for recurring styes. When the eyelid edges are constantly irritated, the oil glands don’t drain properly, creating an environment where bacteria thrive. People with skin rosacea are particularly susceptible. Ocular rosacea, sometimes called meibomian gland dysfunction, causes ongoing inflammation of the oil glands in the eyelids and is directly associated with repeated styes.
Incomplete Makeup Removal
Going to sleep without fully removing eye makeup leaves residue sitting on gland openings overnight. Over time, this residue mixes with dead skin cells and natural oils, forming a plug that blocks the gland. Once blocked, bacteria already present on the lid have hours in a warm, enclosed space to multiply.
Stye vs. Chalazion
For the first day or two, a stye and a chalazion look identical: a tender, swollen bump on the eyelid. After that initial window, they diverge. A stye stays painful and localizes to the eyelid margin, often developing a visible pus-filled head near a lash. You may also notice tearing, light sensitivity, or a gritty feeling as if something is in your eye.
A chalazion, by contrast, migrates toward the body of the eyelid and becomes a firm, painless nodule. Chalazia form when a blocked gland triggers inflammation without an active bacterial infection. It’s common for a stye that doesn’t fully drain to turn into a chalazion over time.
How Long a Stye Lasts
Most styes resolve on their own within two to five days, though some last a week or longer. Warm compresses are the standard home treatment: a clean, warm cloth held against the closed eyelid for 10 to 15 minutes several times a day helps the blocked gland open and drain. Don’t squeeze or pop the stye, as that can spread the infection deeper into the eyelid.
If the stye hasn’t started to shrink after about two days of warm compresses, or if it persists beyond a week, you may need antibiotic treatment. Blurry vision is a reason to seek care promptly, as it can mean the swelling is pressing against the eye itself. Persistent eye pain also warrants a visit.
Why Some People Get Styes Repeatedly
If you’ve had more than one or two styes, the cause is almost certainly an underlying condition rather than bad luck. Chronic blepharitis is the most common culprit. The ongoing low-grade inflammation keeps glands partially blocked, so any minor bacterial exposure can tip into a full infection. Ocular rosacea works the same way, with the added factor that the oil glands themselves produce thicker secretions that are more prone to clogging.
People with dandruff or seborrheic dermatitis also tend toward recurrent styes, because the same overproduction of skin oils that causes flaking on the scalp affects the eyelid glands. Managing the underlying skin condition, whether through lid hygiene routines, prescribed lid scrubs, or treatment for rosacea, is typically what breaks the cycle of repeated styes rather than treating each one individually.