A red eye is almost always caused by dilated or broken blood vessels on the surface of the eye, and the vast majority of cases are harmless. The most common culprits are dry eyes, irritation from allergens or screens, a burst blood vessel, or a mild infection like pink eye. That said, certain combinations of redness with pain or vision changes point to conditions that need prompt attention.
A Bright Red Patch: Broken Blood Vessel
If you see a vivid, well-defined red spot on the white of your eye rather than general pinkness, you likely have a subconjunctival hemorrhage. This is a tiny blood vessel that popped just beneath the surface. It looks alarming but is painless and doesn’t affect your vision at all.
Common triggers include coughing, sneezing, straining, vomiting, rubbing your eye, or a minor bump. Sometimes it happens for no obvious reason, especially during sleep. The spot typically clears on its own within a few days to a few weeks, shifting from red to yellow as the blood reabsorbs, much like a bruise on your skin.
In younger people, a burst vessel is usually caused by minor physical strain or rubbing. In people over 50, recurrent episodes may be linked to high blood pressure or diabetes. One study found that unexplained subconjunctival hemorrhages in older adults can actually be an early predictor of future hypertension. Blood-thinning medications like aspirin or warfarin also raise the risk. If you get these frequently and aren’t sure why, it’s worth having your blood pressure checked.
General Pinkness or Redness: Conjunctivitis
Pink eye (conjunctivitis) is the most common cause of diffuse redness across the white of the eye. There are three main types, and the discharge your eye produces is the easiest way to tell them apart.
- Viral conjunctivitis causes moderate redness with a watery discharge and a gritty, sandy feeling, as if something is stuck in your eye. Light sensitivity is common. This type is highly contagious and typically runs its course in one to two weeks.
- Bacterial conjunctivitis produces a thick yellow or green discharge that can crust your eyelashes shut overnight. The eye may look dramatically red and swollen, but pain is usually mild.
- Allergic conjunctivitis triggers clear, watery discharge along with mild redness. Itching is the hallmark symptom, sometimes intense. Both eyes are typically affected. It tends to flare with pollen, pet dander, or dust.
Dry Eyes and Screen Time
If your eyes feel tired, scratchy, and mildly red, especially later in the day, dry eye is a likely explanation. When the tear film covering your eye becomes unstable, it exposes the surface to friction and air. The body responds with inflammation, which shows up as redness.
Screen use is one of the biggest modern contributors. When you focus on a screen, your blink rate drops significantly, which means the tear film doesn’t get refreshed as often as it should. Over hours, this leads to irritation, redness, and that burning or gritty sensation. The American Optometric Association recommends the 20-20-20 rule: every 20 minutes, look at something 20 feet away for 20 seconds. Consciously blinking more often while working at a screen also helps keep the surface of the eye moist.
Other common dry eye triggers include air conditioning, heating, ceiling fans blowing toward your face, low humidity, and aging. Contact lens wearers are particularly susceptible, since the lens sits on top of the tear film and can disrupt it further.
Contact Lens Complications
Wearing contact lenses introduces specific risks beyond ordinary dry eye. A condition called contact lens-induced acute red eye (CLARE) causes noticeable redness and irritation, often from overwearing lenses or sleeping in them. More seriously, contact lenses can cause corneal infiltrates, which are inflammatory responses in the clear front layer of the eye that may signal early infection. Over time, poorly fitted or overworn lenses can also trigger new blood vessel growth across the cornea, adding a persistent red tinge.
If you wear contacts and your eye turns red, removing the lens is the first step. If the redness doesn’t clear within a few hours, or if it came with pain or blurred vision, the lens may have caused a scratch or infection on the cornea that needs treatment.
Painful Redness: When It’s More Serious
Most red eyes are painless or mildly uncomfortable. Pain changes the picture. These conditions pair redness with significant pain and often reduced vision.
A corneal abrasion, essentially a scratch on the surface of the eye, causes sharp pain, tearing, and light sensitivity. This commonly happens from a fingernail, a tree branch, or a piece of debris. Vision may be blurry if the scratch sits near the center of the cornea.
Iritis (inflammation of the colored part of the eye) produces a constant, deep ache that can radiate into the brow and temple. The eye is red, sensitive to light, and vision is often noticeably dimmer. Scleritis, inflammation of the tough white wall of the eye itself, causes a severe, boring pain that worsens with eye movement and can intensify at night. Left untreated, scleritis can cause permanent vision loss.
Acute angle-closure glaucoma is rare but urgent. It causes sudden, severe throbbing pain in one eye along with a dramatic drop in vision. The cornea may look hazy or steamy. Some people also experience nausea, headache, or see halos around lights. This is a medical emergency requiring same-day treatment to prevent irreversible damage.
Red Flags That Need Prompt Attention
A red eye that is painless, has no discharge, and doesn’t affect your vision will almost always resolve on its own. But certain symptoms in combination with redness warrant a same-day or next-day visit to an eye care provider:
- Significant pain, not just mild irritation but a deep ache or sharp, persistent discomfort
- Reduced or blurry vision that doesn’t clear with blinking
- Sensitivity to light strong enough to make you squint or avoid well-lit rooms
- A pupil that looks irregular or a different size than the other eye
- Recent eye surgery or trauma, especially redness appearing 7 to 10 days after cataract surgery, which could signal a serious internal infection
- Redness that doesn’t improve after a week, or gets steadily worse over several days
Flashing lights, a sudden shower of new floaters, or a dark shadow creeping across your vision alongside a red eye could point to a retinal detachment, which needs evaluation within 24 hours even if the eye itself isn’t painful.
Simple Causes Worth Ruling Out
Before assuming the worst, consider the mundane triggers that account for most red eyes. Smoke, chlorine from swimming, dust, wind, lack of sleep, alcohol, and even a particularly forceful sneeze can temporarily redden the eye. Blepharitis, a chronic low-grade inflammation along the eyelid margin, is another extremely common cause of persistent mild redness and irritation. It often presents as crusty, flaky skin at the base of the eyelashes and responds well to warm compresses and gentle lid hygiene.
Episcleritis, inflammation of the thin tissue layer just over the white of the eye, causes a localized patch of redness with little or no pain. It looks concerning but typically resolves on its own without treatment, similar to a subconjunctival hemorrhage but with a slightly pinkish rather than bright red appearance.