A red eye is almost always caused by dilated or broken blood vessels on the surface of the eye, and in most cases the cause is minor: allergies, dryness, irritation, or a small burst vessel. But certain combinations of symptoms, especially pain, vision changes, or nausea, signal something more serious that needs prompt attention.
The Most Common Causes
The majority of red eyes fall into a handful of categories. Conjunctivitis (pink eye) is the one most people think of first, but dry eyes, allergies, and broken blood vessels on the eye’s surface are just as common. Less frequently, redness comes from inflammation deeper in the eye, an infection of the cornea, or a spike in eye pressure from glaucoma.
What matters most is figuring out which category your redness falls into, because the cause determines whether you can manage it at home or need to see someone quickly.
Pink Eye: Viral, Bacterial, or Allergic
Conjunctivitis is inflammation of the thin, clear membrane covering the white of your eye. The three types look and feel different enough that you can often narrow it down yourself.
Viral conjunctivitis is the most common form. It typically starts in one eye and spreads to the other within a day or two. You’ll notice watery discharge, a gritty feeling, and general redness. It runs its course in one to three weeks, much like a cold. There’s no treatment that speeds it up.
Bacterial conjunctivitis produces thicker, yellow-green discharge that can crust your eyelids shut overnight. It often affects one eye more than the other. Antibiotic eye drops shorten the duration, but mild cases sometimes clear on their own within a week or so.
Allergic conjunctivitis is the itchy one. Both eyes are usually affected at the same time, the discharge tends to be watery and clear, and you’ll likely have other allergy symptoms like sneezing or a runny nose. Over-the-counter allergy eye drops containing antihistamines and mast cell stabilizers (sold under brands like Pataday) are effective. The once-daily formulation goes in each affected eye once per day, while the twice-daily version should be spaced at least six to eight hours apart.
Dry Eyes and Eyelid Inflammation
Chronic redness that comes and goes, especially with burning, stinging, or a sandy sensation, often points to dry eye. Your tear film isn’t lubricating the surface properly, so the tiny blood vessels on the white of your eye dilate in response to the irritation.
A related and often overlooked cause is blepharitis, which is inflammation along the eyelid margins. Bacteria naturally live on your eyelids, but over time they form a sticky layer called a biofilm along the lash line. As the bacterial colony grows, it releases inflammatory compounds that irritate the oil glands in your eyelids. Those glands normally contribute an oily layer to your tears that keeps them from evaporating too fast. When the glands get clogged and inflamed, tear quality drops, and your eyes become chronically red, dry, and irritated.
This is why people with persistent low-grade redness often find that artificial tears alone aren’t enough. Keeping the eyelids clean with warm compresses and gentle lid scrubs addresses the root problem by breaking up that bacterial buildup.
A Bright Red Patch: Broken Blood Vessel
If you woke up with a vivid, blood-red spot on the white of your eye but no pain or vision changes, you’re probably looking at a subconjunctival hemorrhage. A tiny blood vessel under the surface popped, and blood pooled beneath the clear membrane. It looks alarming but is almost always harmless.
Common triggers include coughing, sneezing, vomiting, straining on the toilet, heavy lifting, rubbing your eye too hard, or wearing contact lenses. Blood-thinning medications also make it more likely. Less commonly, it’s linked to diabetes, high blood pressure, or clotting disorders.
These typically clear on their own within a few weeks. The red spot may shift colors, turning yellowish or greenish as the blood absorbs, similar to a bruise. No drops or treatment are needed. If it keeps happening, though, it’s worth checking your blood pressure and talking to a doctor about possible underlying causes.
Deeper Inflammation: Uveitis and Scleritis
Not all redness is on the surface. Uveitis is inflammation of the middle layer of the eye wall, and scleritis is inflammation of the sclera, the tough white outer shell. Both produce redness that looks different from pink eye. The redness is often deeper in color, sometimes with a purplish or bluish tint, and it doesn’t produce the same watery or goopy discharge.
The key distinguishing feature is pain. Scleritis often causes a piercing, deep ache that gets worse when you move your eye. Uveitis can cause light sensitivity, blurred vision, and floaters in addition to pain. Both conditions require professional treatment because they can damage vision if left alone. Scleritis is sometimes associated with autoimmune conditions like rheumatoid arthritis.
When Red Eye Is an Emergency
Most red eyes are not emergencies, but a few specific patterns demand immediate care. Acute angle-closure glaucoma causes sudden, severe eye pain along with redness, headache, nausea or vomiting, blurred vision, and seeing rainbow-colored halos around lights. Pressure inside the eye spikes rapidly and can cause permanent vision loss within hours if untreated.
Go to an emergency room or call your eye doctor immediately if your red eye comes with any of these:
- Sudden changes in your vision
- Severe eye pain, especially with headache, fever, or light sensitivity
- Nausea or vomiting alongside eye symptoms
- A chemical splash or foreign object in the eye
- Halos or rings around lights that weren’t there before
- Swelling in or around the eye
- Inability to open or keep your eye open
What You Can Do at Home
For mild redness from allergies, dryness, or viral conjunctivitis, simple home care goes a long way. Compresses are one of the most effective tools, and choosing warm versus cold depends on what’s going on. Cold compresses (a cool, damp washcloth over closed eyes) help with itching and inflammation, making them ideal for allergic reactions. Warm compresses help loosen crusty discharge and unclog oil glands along the eyelids, so they’re better for bacterial conjunctivitis and blepharitis. Applying either type three or four times a day for several minutes at a time is a standard recommendation.
Preservative-free artificial tears can soothe dryness and flush out mild irritants. If you wear contact lenses, take them out until the redness resolves.
Avoid Redness-Relieving Drops for More Than 3 Days
Over-the-counter drops marketed specifically to “get the red out” work by constricting blood vessels on the eye’s surface. Most contain a decongestant called tetrahydrozoline. They do make your eyes look whiter temporarily, but when the effect wears off, your blood vessels can dilate even more than before. This rebound redness tends to worsen with repeated use, eventually leaving your eyes persistently red. The American Academy of Ophthalmology recommends not using these drops for more than 72 hours. They mask the symptom without addressing the cause, and they can make things worse over time.
If your redness isn’t improving after a week of home care, is getting worse, or is accompanied by pain or vision changes, it’s time for a professional evaluation. Many causes of red eye are straightforward to treat once correctly identified.