A red eye is almost always caused by dilated or irritated blood vessels on the surface of the eye. The most common reasons are allergies, dry eye, a minor infection, or a burst blood vessel, and most cases resolve on their own or with simple treatment. But certain combinations of symptoms, especially eye pain, vision changes, or sensitivity to light, signal something more serious that needs prompt attention.
Conjunctivitis (Pink Eye)
Pink eye is the single most common cause of eye redness, and it comes in three forms that look and feel noticeably different from each other.
Viral conjunctivitis produces a clear, watery discharge along with a gritty sensation, as if something is stuck in your eye. It typically starts in one eye and spreads to the other within a day or two. You’ll often have cold or flu-like symptoms at the same time. Swollen eyelids and light sensitivity are common. There’s no antibiotic treatment for viral pink eye; it clears up on its own, usually within one to two weeks.
Bacterial conjunctivitis is the version that produces a thick, yellow or greenish discharge. Your eyelids may stick together after sleep. It can affect one or both eyes and often responds well to antibiotic eye drops.
Allergic conjunctivitis is easy to distinguish because it affects both eyes simultaneously and causes intense itching. You’ll likely have other allergy symptoms too, like sneezing or a runny nose. The discharge is mostly just excessive tearing rather than anything thick or colored. Over-the-counter antihistamine eye drops typically provide relief.
Dry Eye
If your eyes are chronically red, especially later in the day or after screen time, dry eye is a leading suspect. When your tear film breaks down or evaporates too quickly, the surface of the eye becomes irritated. This triggers inflammation, which causes the tiny blood vessels in the white of your eye to widen. Those dilated vessels increase blood flow to the area, producing visible redness.
The cycle tends to feed itself. Inflammation makes the tear film even less stable, which causes more irritation, which drives more inflammation. Over time, this can become a chronic condition. Common contributors include prolonged screen use (you blink less often while staring at screens), dry indoor air, contact lens wear, and aging. Artificial tears can help break the cycle for mild cases, but persistent dry eye sometimes needs prescription treatment to address the underlying inflammation.
Burst Blood Vessel
If you woke up with a bright red patch on the white of your eye that looks alarming but doesn’t hurt, you likely have a subconjunctival hemorrhage. This is a small blood vessel that broke just beneath the surface. It looks dramatic but is almost always harmless.
Common triggers include coughing, sneezing, vomiting, straining on the toilet, lifting something heavy, rubbing your eye too hard, or wearing contact lenses. Blood thinners also increase the risk. Most subconjunctival hemorrhages heal within two weeks without any treatment. The red patch may shift color (like a bruise) as it fades.
Contact Lens Problems
Contact lenses show up as a risk factor for nearly every type of eye redness. They can cause dry eye by disrupting your tear film, introduce bacteria that lead to infection, and even create small scratches on the cornea. Overwearing lenses, sleeping in them, or not cleaning them properly all increase the odds of redness and irritation.
A corneal ulcer is one of the more serious contact lens complications. This is an open sore on the clear front surface of the eye, and it can permanently damage your vision or cause blindness if left untreated. Other risk factors for corneal ulcers include a history of cold sores, chicken pox, or shingles, as well as using steroid eye drops. If you wear contacts and develop eye pain, not just irritation, remove your lenses and get it checked.
Redness-Relieving Drops Can Backfire
If you’ve been using over-the-counter drops to “get the red out,” they may actually be making the problem worse. Most redness-relieving drops contain a decongestant called tetrahydrozoline, which works by temporarily shrinking the blood vessels on your eye’s surface. When the drops wear off, those blood vessels can dilate even more than before, a phenomenon called rebound redness. Over time, this creates a cycle where you need the drops more frequently and the redness between doses gets progressively worse.
A newer ingredient called brimonidine works through a different mechanism and carries a lower risk of rebound redness. But the better approach for most people is to treat the underlying cause of the redness rather than masking it with drops. Artificial tears (the lubricating kind, not the redness-reducing kind) are a safer choice for general irritation.
More Serious Causes of Eye Redness
Most red eyes are minor, but a few conditions require urgent care.
Scleritis is inflammation of the sclera, the tough white outer layer of the eye. It causes a piercing pain that worsens when you move your eye, and it can be severe enough to wake you from sleep. The pain sometimes spreads to other parts of your face. Unlike pink eye, which may cause mild discomfort, scleritis produces deep, intense pain. It often occurs alongside autoimmune conditions and needs prescription treatment to prevent complications.
Uveitis is inflammation of the layer just beneath the sclera. It can occur at the same time as scleritis, though they’re separate conditions. Symptoms include redness, pain, light sensitivity, and blurred vision. Left untreated, uveitis can lead to permanent vision loss.
Acute angle-closure glaucoma is a medical emergency. It happens when pressure inside the eye rises rapidly, often exceeding 40 mmHg (normal is 10 to 21). Symptoms come on suddenly: blurred vision, a red eye, severe eye pain, headache, nausea, and vomiting. You may see halos or rings around lights. Without prompt treatment, the high pressure can cause irreversible damage to the optic nerve. This is one reason eye redness paired with vision changes or severe pain always warrants immediate care.
When Eye Redness Needs Immediate Attention
Most red eyes don’t need an emergency visit. But certain symptoms alongside redness indicate something that can’t wait. Seek immediate care if:
- Your vision changes suddenly
- You have a severe headache, eye pain, fever, or light sensitivity along with the redness
- You feel nauseated or are vomiting
- A chemical or foreign object got into your eye
- You see halos or circles around lights
- You have swelling in or around the eye
- You can’t open your eye or keep it open
Red eye without pain, vision changes, or light sensitivity is rarely an emergency. But if it lasts more than a week or two without improving, or keeps coming back, it’s worth getting an evaluation to identify the underlying cause rather than continuing to treat the symptom alone.