Red in your eye usually comes from one of two things: a broken blood vessel on the surface of the eye, which looks like a bright red patch, or dilated blood vessels across the white of the eye, which creates a more diffuse pink or bloodshot appearance. Most causes are harmless and resolve on their own, but a few combinations of symptoms signal something that needs prompt attention.
A Bright Red Patch: Subconjunctival Hemorrhage
If the redness looks like a well-defined, vivid red spot rather than general bloodshot irritation, you’re likely looking at a subconjunctival hemorrhage. A tiny blood vessel on the surface of your eye burst, and blood pooled under the clear membrane covering the white part. It looks alarming but causes no pain, no discharge, and no vision changes.
These happen more often than most people realize. Common triggers include coughing, sneezing, vomiting, straining on the toilet, or rubbing your eye too hard. Contact lens wear and blood-thinning medications also increase the risk. Sometimes there’s no identifiable cause at all. The red patch typically clears on its own within two to three weeks as your body reabsorbs the blood, shifting from bright red to yellow-green before fading completely. No treatment is needed.
If you get subconjunctival hemorrhages repeatedly without an obvious trigger, it’s worth having your blood pressure and clotting checked. Diabetes, high blood pressure, and blood clotting disorders can make these episodes more frequent.
General Bloodshot Redness: The Likely Culprits
When your eye looks broadly pink or bloodshot rather than having a distinct red spot, the blood vessels across the surface of your eye are inflamed and dilated. The most common reasons fall into a few categories.
Conjunctivitis (Pink Eye)
Pink eye is the single most common cause of a red, irritated eye. It comes in three forms, and the type of discharge is the biggest clue to which one you have. Viral conjunctivitis produces a watery, clear discharge and often starts in one eye before spreading to the other within a day or two. It’s very contagious and typically runs its course in one to two weeks. Bacterial conjunctivitis produces thicker, yellowish or greenish discharge. The hallmark sign is waking up with your eyelids crusted or glued shut. It’s also very contagious. Allergic conjunctivitis causes intense itching in both eyes with watery or stringy discharge. Unlike the other two types, it isn’t contagious and tends to flare alongside other allergy symptoms like sneezing or a runny nose.
Dry Eye
Dry eye causes chronic, low-grade redness that comes and goes, often alongside a gritty or sandy feeling, mild stinging, and paradoxically, episodes of excessive watering. When your tear film becomes unstable, the surface of the eye gets irritated and triggers an inflammatory cycle. Blood vessels in the conjunctiva widen, increasing blood flow to the area, which is what produces that persistent pinkish look. Both eyes are usually affected. Screen use, dry indoor air, aging, and certain medications all contribute.
Blepharitis
If the redness is concentrated along your eyelid margins and you notice flaky, dandruff-like debris at the base of your eyelashes, blepharitis is a strong possibility. It’s a chronic inflammation of the eyelids that tends to be worse in the morning. The irritation it causes can make the eye itself look red and feel gritty.
Contact Lens Wearers: Pay Extra Attention
If you wear contacts and your eye is red, take the lens out. Contact lenses create a unique set of risks because they sit directly on the cornea and can trap bacteria, reduce oxygen flow, and cause microabrasions. Sleeping in contacts, swimming with them in, or cleaning them with tap water significantly raises your risk of a corneal ulcer, a bacterial infection on the surface of the cornea.
Symptoms of a corneal ulcer include a red, watery eye with severe pain, blurred vision, pus-like discharge, and sometimes a visible white or gray spot on the cornea (though this can be hard to see without magnification). A parasitic infection called Acanthamoeba keratitis is a particular danger for contact lens wearers who swim or use tap water on their lenses. Any red eye with pain or vision changes while wearing contacts warrants same-day evaluation.
Less Common but More Serious Causes
Several conditions produce a red eye alongside symptoms that clearly signal something deeper is going on. These are less likely, but recognizing the pattern matters.
Uveitis (Iritis)
Uveitis is inflammation inside the eye, most commonly affecting the front chamber between the cornea and the iris. It causes a constant aching pain that can radiate into the brow or temple, sensitivity to light, blurred vision, and sometimes dark floating spots. The pupil on the affected side may appear smaller and react sluggishly to light. This requires treatment to prevent lasting damage to vision.
Episcleritis and Scleritis
Episcleritis produces a localized wedge-shaped patch of redness with little to no pain and no light sensitivity. It looks concerning but is generally mild and self-limiting. Scleritis, by contrast, involves deep, boring pain that can interfere with sleep and worsens with eye movement. The distinction matters because scleritis is often associated with underlying autoimmune conditions and can threaten vision if untreated.
Acute Angle-Closure Glaucoma
This is the one true emergency on this list. It happens when fluid drainage inside the eye suddenly blocks, causing pressure to spike rapidly. Symptoms come on fast: severe throbbing eye pain, a bad headache, nausea or vomiting, blurred vision, halos or colored rings around lights, and a red eye. The eyeball itself may feel firm and tender to the touch. This requires emergency treatment within hours to prevent permanent vision loss.
Corneal Abrasion or Foreign Body
A scratch on the cornea or a small particle stuck under the eyelid causes sharp pain, a strong foreign body sensation, watering, light sensitivity, and difficulty keeping the eye open. If you felt something hit or enter your eye before the redness started, this is the most likely explanation.
Symptoms That Need Immediate Attention
Most red eyes are benign, but certain symptom combinations point to conditions that can permanently affect your vision if treatment is delayed. Seek immediate care if your redness comes with any of the following: sudden changes in vision, severe eye pain or headache, sensitivity to light, nausea or vomiting, halos around lights, a feeling that something is stuck in your eye that you can’t flush out, swelling in or around the eye, or inability to open or keep the eye open. Redness caused by a chemical splash or an object striking the eye also warrants emergency evaluation regardless of how the eye feels afterward.
A painless red eye with no vision changes and no discharge beyond mild watering is almost always something that will resolve on its own or with simple measures like lubricating drops. Pain, vision loss, and light sensitivity are the three symptoms that consistently separate routine causes from conditions requiring urgent care.