Styes are caused by bacterial infection of the tiny oil glands or hair follicles along your eyelid margin. The culprit is almost always Staphylococcus aureus, a common bacterium that lives on your skin and can colonize a blocked gland, triggering a painful, red bump. Most styes resolve on their own within one to two weeks, but understanding what causes them helps you prevent recurrences.
How a Stye Forms
Your eyelids contain dozens of small glands that produce oils to keep your eyes lubricated. When one of these glands gets clogged with dead skin cells, dried oil, or debris, bacteria that normally live harmlessly on your skin can multiply inside the blocked gland. The result is a localized infection: swelling, redness, tenderness, and often a visible pus-filled bump near the lash line.
There are two types, depending on which gland is affected. An external stye (the most common kind) develops when an eyelash follicle or one of the small oil glands right at the base of a lash becomes infected. An internal stye forms deeper in the eyelid when one of the larger oil-producing glands embedded in the eyelid tissue gets infected. Internal styes tend to be more painful and may point inward toward the eye rather than forming a visible bump on the outer lid.
Everyday Habits That Raise Your Risk
The most common trigger is simply touching your eyes with unwashed hands. Every time you rub your eyes, adjust your lashes, or put in contact lenses without clean hands, you introduce bacteria to an area rich in vulnerable glands.
Eye makeup is another frequent contributor. Liquid and cream products like mascara, liquid eyeliner, and concealer are especially risky because their moisture encourages bacterial growth. One study found that 90% of used makeup products harbor significant bacteria, including strains capable of causing infection. Sharing eye makeup, sleeping in it, or using products past their shelf life all increase the chance of transferring bacteria directly into your lash follicles.
Contact lens wearers face additional risk if they skip proper hygiene steps. The CDC recommends washing and fully drying your hands before handling lenses, rubbing and rinsing lenses with fresh disinfecting solution each time, never topping off old solution in your case, and replacing your lens case at least every three months. Shortcuts with any of these steps can introduce bacteria to the eyelid surface.
Chronic Conditions That Cause Recurring Styes
If you keep getting styes, the problem is likely an underlying condition rather than a one-time hygiene lapse. Blepharitis, a chronic inflammation of the eyelid margins, is one of the most common causes of recurrent styes. It keeps the oil glands in a state of low-grade irritation and blockage, creating a perfect environment for repeated infections.
Ocular rosacea is another major driver. This condition inflames the eyelids and disrupts the oil glands, leading to what’s called meibomian gland dysfunction. When these glands can’t produce healthy oils, the tear film becomes unstable, and the eyelid margin stays irritated and prone to infection. People with rosacea on their facial skin are particularly likely to develop the ocular form as well.
Microscopic mites called Demodex also play a role that most people don’t know about. These tiny organisms (about 0.2 to 0.3 mm long) live in the oil glands and hair follicles of almost everyone’s eyelids, usually without causing problems. But when their numbers grow too large, they physically block the gland openings and trigger inflammation. Their outer shells provoke an immune response that can lead to chronic eyelid irritation and recurring bumps.
Stress, Sleep, and Your Immune System
No study has directly proven that stress causes styes, but many eye specialists report seeing the connection in their patients. The likely explanation is indirect: stress hormones suppress your immune system’s ability to keep bacteria in check. A 2017 study found that stress hormones can be converted into compounds that actually help attract bacteria to susceptible areas of the body.
Sleep deprivation works through a similar pathway. Poor sleep reduces the effectiveness of T cells, immune cells that fight off infections. There’s also a practical side to it. When you’re exhausted, you’re less likely to wash your hands before rubbing your eyes, less likely to remove makeup before bed, and more likely to skip the small hygiene steps that keep eyelid bacteria under control.
Styes vs. Chalazions
Not every eyelid bump is a stye. A chalazion looks similar but develops differently. Styes are acute infections: they come on fast, hurt from the start, and typically involve redness and a visible pus point. A chalazion is a blocked oil gland that becomes inflamed without active infection. It tends to be firmer, less painful, and slower to develop. An internal stye can sometimes turn into a chalazion if the infection resolves but the gland remains blocked.
The distinction matters because treatment differs. Styes usually respond to warm compresses and resolve within days to a couple of weeks. Chalazions can linger for months and sometimes need professional drainage.
How Long Styes Last
Left alone, most styes resolve on their own in one to two weeks. You can speed that up by applying a warm compress for about 15 minutes, four times a day. The heat opens the blocked gland, softens the trapped oil, and encourages the stye to drain. When you start warm compresses, the bump may temporarily look larger before it pops and drains on its own within a few days.
Resist the urge to squeeze or pop a stye yourself. Forcing it can push the infection deeper into the tissue or spread bacteria to neighboring glands.
When a Stye Becomes Serious
Styes rarely cause complications, but infection can occasionally spread to the surrounding skin. This leads to a condition called preseptal cellulitis, where the tissue around the eye socket becomes swollen, red, and warm. If the infection spreads even deeper, past the tissue barrier protecting the eye socket, it becomes orbital cellulitis, a much more dangerous situation.
Warning signs that a stye has progressed beyond a simple bump include fever alongside eye pain and swelling, vision changes, swelling that extends well beyond the eyelid, and any bulging of the eye itself. These symptoms call for immediate medical attention, particularly in children, who are more susceptible to rapid spread of eyelid infections.
Preventing Styes
Most styes are preventable with consistent eyelid hygiene. Wash your hands before touching your eyes or handling contact lenses. Replace mascara and liquid eyeliner every three months, and never share eye makeup. Remove all eye makeup before bed, even when you’re tired.
If you’re prone to recurrent styes, a daily lid-cleaning routine can make a real difference. Warm compresses for a few minutes each morning help keep the oil glands flowing freely. Gently cleaning the lash line with diluted baby shampoo or a dedicated eyelid cleanser removes the debris and bacterial buildup that lead to blockages. For people with blepharitis or rosacea, treating the underlying condition is the single most effective way to break the cycle of repeat infections.