A red eye happens when tiny blood vessels on the surface of your eye dilate or, less commonly, burst. The most likely cause is something minor like irritation, dryness, or an infection, but the specific pattern of redness, along with any other symptoms you’re experiencing, helps narrow down what’s going on.
How Eyes Turn Red
The white part of your eye is covered by a thin, clear membrane called the conjunctiva, which is packed with small blood vessels. When those vessels expand, more blood flows through them and the white of your eye looks pink or red. Because these vessels sit right at the surface, even a small amount of inflammation makes them very visible. This dilation can be triggered by infection, allergens, dryness, physical irritation, or internal inflammation deeper in the eye.
Conjunctivitis (Pink Eye)
Conjunctivitis is the single most common reason for a red eye. It comes in three main forms, and the type of discharge you’re producing is the easiest way to tell them apart.
Viral conjunctivitis usually starts in one eye and spreads to the other within a day or two. It produces a watery, clear discharge and often accompanies a cold or upper respiratory infection. There’s no antibiotic that speeds it up. It resolves on its own, typically within one to two weeks.
Bacterial conjunctivitis tends to produce thicker, yellow or green discharge that can crust your eyelids shut overnight. Most acute cases also clear within one to two weeks without treatment, though antibiotic eye drops can shorten that timeline. If you notice massive swelling, severe discharge, pain, or any drop in vision, that points to a more aggressive bacterial infection that needs prompt treatment.
Allergic conjunctivitis almost always affects both eyes at once and itching is the dominant symptom. You’ll likely notice watery eyes and puffiness rather than thick discharge, and symptoms tend to flare with pollen, pet dander, or dust exposure.
A Bright Red Patch: Broken Blood Vessel
If your redness looks less like pink eye and more like a solid, bright red blotch on the white of your eye, you’re probably looking at a subconjunctival hemorrhage. This is a tiny blood vessel that popped and bled under the surface. It looks alarming but is almost always harmless.
Common triggers include sneezing, coughing, vomiting, straining on the toilet, heavy lifting, or rubbing your eye too hard. Contact lens wear and blood-thinning medications can also cause them. Sometimes there’s no identifiable cause at all, especially in people with high blood pressure or diabetes. These typically resolve on their own within a few weeks as the blood is gradually reabsorbed. There’s no pain or vision change, just the dramatic appearance.
Dry Eyes and Screen Time
Chronic dryness is one of the most underappreciated causes of persistent redness. When your eye’s surface doesn’t stay moist enough, it becomes irritated and those surface blood vessels dilate in response. No single test diagnoses dry eye disease on its own. It’s identified through a combination of symptoms and clinical findings.
Screen use is a major contributor. You normally blink about 15 times per minute, but that rate drops by roughly half when you’re staring at a screen or reading. Less blinking means your tear film evaporates faster, leaving the surface exposed. This won’t permanently damage your eyes, but it causes real discomfort, redness, and a gritty or burning feeling that tends to worsen over the course of the day. The 20-20-20 rule helps: every 20 minutes, look at something 20 feet away for 20 seconds. Artificial tears can also provide relief.
Contact Lens Problems
If you wear contact lenses and your eye has turned red, take the lens out. Contact lens wear is a primary risk factor for corneal infections, and the risk climbs significantly with overnight use, poor hygiene, or skipping proper cleaning solutions.
Simple overwear often causes temporary redness and irritation that improves within hours of removing the lens. A corneal ulcer, however, is a more serious infection of the cornea itself. Warning signs include increasing pain, light sensitivity, blurred vision, and a white or gray spot on the cornea. Ulcers near the center of the cornea or larger than about 2 millimeters are particularly concerning because they can threaten your vision. Redness from contact lenses that doesn’t improve after removing them, or that comes with pain and vision changes, warrants a same-day eye exam.
Uveitis: Inflammation Inside the Eye
Uveitis is inflammation of the middle layer of the eye wall, and it produces a distinct combination of symptoms: redness, eye pain, light sensitivity, blurred vision, and dark floating spots. The most common form, called anterior uveitis, affects the front of the eye near the iris. Unlike conjunctivitis, uveitis doesn’t produce significant discharge.
Symptoms can come on suddenly and worsen quickly, or they can develop gradually. In some cases, uveitis is found during a routine eye exam before a person even notices symptoms. It’s sometimes linked to autoimmune conditions, infections, or eye injuries, but it can also occur without a clear cause. Uveitis requires treatment to prevent complications like vision loss.
When Redness Signals an Emergency
Most red eyes are benign and short-lived. But certain combinations of symptoms point to conditions that can permanently damage your vision if not treated quickly.
Acute angle-closure glaucoma causes sudden, severe eye pain along with redness, blurred or lost vision, halos or rainbow-colored rings around lights, headache, and nausea or vomiting. This happens when fluid drainage inside the eye becomes blocked, causing pressure to spike rapidly. It’s a true emergency.
Seek immediate care if your red eye is accompanied by any of these:
- Severe pain in or around the eye
- Any change in vision, including blurriness, double vision, or partial vision loss
- Nausea or headache alongside eye pain
- A chemical splash or penetrating injury to the eye
- A visible scratch or cut on the eyeball
Figuring Out Your Cause
A few quick questions can help you sort through the possibilities. Is there discharge, and if so, what kind? Thick and colored points toward bacterial infection. Watery and itchy suggests allergies. Is there pain? Surface irritation feels gritty or scratchy, while deeper inflammation or pressure problems cause aching or throbbing pain. Is your vision affected at all? Any blurriness, light sensitivity, or floaters moves the situation from “probably minor” to “get it checked.”
Redness that’s mild, painless, and not affecting your vision, especially if it follows an obvious trigger like a late night, dry air, allergies, or long screen time, will typically resolve within a few days with basic care like artificial tears and rest. Redness that persists beyond two weeks, keeps coming back, or arrives with pain or vision changes deserves a professional evaluation to rule out something deeper.