Styes are caused by bacterial infection of the tiny oil or sweat glands along your eyelid margin. The culprit is almost always Staphylococcus aureus, a common bacterium that normally lives on your skin without causing problems. When it gets trapped inside a blocked gland, it multiplies, triggers inflammation, and produces the painful red bump you recognize as a stye. Most styes last one to two weeks and resolve on their own.
How a Stye Forms
Your eyelids contain dozens of small glands that produce oils and sweat to keep your eyes lubricated. When one of these glands becomes clogged, bacteria that are already present on your skin can get trapped inside. The bacteria begin to multiply in the warm, sealed environment, and your immune system responds with inflammation: redness, swelling, tenderness, and eventually a small pus-filled bump.
The bacteria don’t just sit passively in the blocked gland. They produce enzymes called lipases that break down the oily secretions into irritating free fatty acids. These byproducts worsen the inflammation and, ironically, create an environment that further promotes bacterial growth. This is why styes can become quite painful before they finally come to a head and drain.
External vs. Internal Styes
Not all styes are the same, and where yours forms depends on which gland is infected. External styes develop at the base of your eyelashes, in the small oil or sweat glands right at the lid margin. These are the most common type and look like a pimple sitting on the edge of your eyelid.
Internal styes form deeper in the eyelid, in the larger oil-producing glands embedded in the firm tissue of the lid itself. Because they’re deeper, internal styes tend to be more painful and may not show an obvious white head on the surface. Instead, you might notice a tender, swollen area that’s more visible when you gently flip the eyelid.
Risk Factors That Make Styes More Likely
Touching Your Eyes
The simplest and most common trigger is transferring bacteria to your eyelids with your hands. Rubbing your eyes, applying contact lenses without washing your hands, or even resting your face in your palms can introduce bacteria directly to the gland openings along your lash line.
Old or Shared Eye Makeup
Eye cosmetics are a surprisingly effective breeding ground for bacteria. One study found that 90% of used makeup products contain significant levels of bacteria, including species like E. coli. Mascara wands and eyeliner pencils make direct contact with your lid margin, depositing bacteria right where gland openings are most vulnerable. Sharing eye makeup multiplies the risk because you’re introducing someone else’s bacterial flora to your own eyelids.
Blepharitis
Blepharitis, a chronic inflammation of the eyelid margins, is one of the strongest predictors of recurrent styes. The condition involves ongoing bacterial colonization along the lid edge, with a heavier-than-normal burden of bacteria constantly present. The bacterial enzymes that break down your eyelid oils into irritating compounds keep the lids inflamed, and that chronic inflammation makes gland blockages far more frequent. If you get styes repeatedly, underlying blepharitis is a likely explanation.
Ocular Rosacea
Rosacea doesn’t just affect the cheeks and nose. When it involves the eyes, a form sometimes called ocular rosacea, it causes chronic eyelid inflammation and dysfunction of the oil glands. Styes and similar bumps called chalazia are among the most common complications. If you have facial rosacea and notice frequent eyelid problems, the two are likely connected.
Diabetes and Immune Suppression
High blood sugar triggers the production of molecules that suppress your body’s immune defenses. This means people with uncontrolled diabetes are more prone to infections in general, and styes specifically. Any condition or medication that weakens your immune response, including chronic stress, sleep deprivation, or immunosuppressive drugs, can tip the balance in favor of the bacteria that cause styes.
Styes vs. Chalazia
A stye and a chalazion can look similar, but they feel very different and arise from different processes. A stye is an active bacterial infection. It’s tender to the touch, appears red and swollen, and often develops a visible pus-filled point within a few days.
A chalazion, by contrast, is not an infection. It forms when an oil gland becomes blocked and the trapped secretions leak into the surrounding tissue, causing a slow inflammatory reaction. The result is a firm, painless nodule that develops gradually and can persist for weeks or months. Sometimes a stye that doesn’t fully drain will transition into a chalazion as the acute infection fades but the blockage remains.
What to Expect as a Stye Heals
Most styes resolve within one to two weeks without any medical treatment. In the first few days, the bump grows more swollen and tender as the infection peaks. Eventually, the stye comes to a head, ruptures or drains on its own, and the pain subsides quickly after that.
The single most effective home treatment is a warm compress. Holding a clean, warm washcloth against your closed eyelid for 10 to 15 minutes several times a day softens the blocked material inside the gland and encourages it to drain naturally. Resist the urge to squeeze or pop a stye. Forcing it open can push the infection deeper into the eyelid tissue or spread bacteria to neighboring glands.
If a stye doesn’t improve after two weeks, grows significantly larger, affects your vision, or spreads redness beyond the immediate bump, it may need to be drained by a doctor through a small incision. This is a quick in-office procedure, but most people never need it.
Why Some People Get Styes Repeatedly
A single stye is usually just bad luck: a gland got clogged, bacteria took advantage, and it resolved. But if you’re getting styes multiple times a year, something is keeping your eyelid glands chronically vulnerable. The most common underlying causes are blepharitis, ocular rosacea, and poorly controlled diabetes.
Daily eyelid hygiene can break the cycle for many people. Gently cleaning the base of your eyelashes each day with warm water or a diluted baby shampoo solution removes the bacterial buildup and oily debris that lead to gland blockages. Replacing eye makeup every few months, avoiding sharing cosmetics, and keeping contact lenses clean are practical steps that reduce bacterial exposure. For people with chronic blepharitis or rosacea, consistent lid hygiene is less of a one-time fix and more of an ongoing routine that keeps flare-ups at bay.