A red eye is almost always caused by dilated or broken blood vessels on the surface of the eye. The most common culprits are viral conjunctivitis (pink eye), dry eye, blepharitis (inflamed eyelids), minor corneal scratches, and burst blood vessels. Most cases resolve on their own or with simple treatment, but a few combinations of symptoms signal something that needs urgent attention.
The Most Likely Causes
If your eye is red but your vision is normal and you’re not in significant pain, the cause is probably one of these common conditions.
Conjunctivitis (pink eye) is the single most frequent reason for red eyes. Viral conjunctivitis produces a watery discharge and often starts in one eye before spreading to the other. Bacterial conjunctivitis tends to produce thicker, yellowish or greenish discharge that may glue your eyelids shut overnight. Three signs that point toward a bacterial cause: waking up with stuck-together lids, no itching, and never having had pink eye before. Both types spread easily through hand-to-eye contact and contaminated surfaces.
Allergic conjunctivitis causes redness in both eyes along with intense itching and clear, watery discharge. It typically follows a seasonal pattern and tends to show up alongside other allergy symptoms like sneezing or a runny nose.
Dry eye creates a gritty, burning sensation and redness that worsens with screen time, wind, or dry indoor air. It’s chronic for many people and responds to lubricating drops (artificial tears, not redness-relief drops).
Blepharitis is inflammation along the eyelid margins, often from clogged oil glands at the base of your lashes. Your eyelids may look crusty or flaky, especially in the morning. It rarely goes away completely and typically requires daily eyelid cleaning to keep under control.
A Bright Red Patch With No Pain
If you looked in the mirror and saw a vivid, well-defined red spot on the white of your eye, you’re likely looking at a subconjunctival hemorrhage. This happens when a tiny blood vessel on the eye’s surface bursts, leaking blood into the space beneath the clear membrane covering the white of your eye. It looks alarming but is painless, doesn’t affect your vision, and clears up on its own in one to two weeks. Larger patches can take up to three weeks to fully fade.
Common triggers include coughing, sneezing, straining, or rubbing your eyes. Sometimes it happens for no obvious reason at all. The blood stays trapped under the surface and gradually reabsorbs, often shifting color from bright red to yellow before disappearing, similar to a bruise.
Scratched Cornea
A corneal abrasion causes redness alongside sharp pain, a persistent feeling that something is stuck in your eye, excessive tearing, and sensitivity to light. It typically follows an obvious event: a fingernail catching your eye, a piece of debris, or sleeping in contact lenses. Your vision may be slightly blurry on the affected side.
An eye care provider diagnoses a scratch by placing a fluorescent dye on the eye’s surface. The dye pools in any damaged area and glows green under a blue light, clearly outlining the abrasion. Most small scratches heal within a few days. If you wear contact lenses and notice a pattern of tiny pinpoint lesions rather than one scratch, that can indicate a lens-related injury.
Contact Lens Risks
Wearing contacts increases your risk of corneal infection, a condition called microbial keratitis, where bacteria, fungi, or even parasites invade the cornea. This risk climbs when lenses are worn too long, slept in, or not cleaned properly. Symptoms include pain, redness, light sensitivity, and discharge. Severe cases can lead to permanent vision loss or the need for a corneal transplant. If you wear contacts and develop a painful red eye, remove the lenses immediately and get evaluated promptly.
When Red Eyes Signal Something Serious
Certain symptom combinations point to conditions that can threaten your vision. The key warning signs are significant pain, sensitivity to light (especially if it hurts when light enters your other eye), decreased vision, and nausea or vomiting alongside eye symptoms.
Acute angle-closure glaucoma is an emergency caused by a sudden spike in pressure inside the eye. Fluid that normally drains through a small channel gets blocked, and pressure builds rapidly. Symptoms come on fast: severe pain in or around one eye, blurred vision, rainbow-colored halos around lights, headache, nausea, and vomiting. The nausea and headache sometimes lead people to think they have a stomach bug or migraine rather than an eye problem. This requires immediate treatment to prevent permanent vision loss.
Uveitis (iritis) is inflammation inside the eye itself, not just on the surface. It causes deep, aching pain, redness concentrated in a ring around the colored part of the eye, light sensitivity, and sometimes blurry vision. It tends to affect one eye at a time and can recur. In some people, uveitis is linked to autoimmune conditions like inflammatory bowel disease, lupus, multiple sclerosis, or rheumatoid arthritis.
Scleritis is inflammation of the tough white outer wall of the eye. The pain is severe, boring, and often worse at night or when you move your eyes. It can radiate into the face. Like uveitis, scleritis is sometimes connected to autoimmune diseases, particularly rheumatoid arthritis.
Why Redness-Relief Drops Can Backfire
Over-the-counter eye drops marketed for redness relief work by constricting the blood vessels on your eye’s surface. The problem is that many of these drops cause rebound redness when you stop using them, meaning your eyes end up redder than they were before. This effect has been documented after as few as 5 to 10 days of daily use with older formulations. In one case series, 70 patients who used these drops daily (averaging nearly four times a day for a median of three years) showed persistent redness, evidence that their blood vessels had stopped responding to the drops or were rebounding.
The FDA requires these products to carry a warning that overuse may increase redness. Newer formulations that work through a different mechanism appear to cause less rebound, but the safest approach for everyday redness is to treat the underlying cause rather than mask the symptom. Lubricating artificial tears help with dry eye and general irritation without the rebound risk.
Patterns That Help Identify the Cause
A few simple observations can help you narrow down what’s going on. Redness in both eyes with itching points toward allergies. Redness in one eye with thick discharge suggests bacterial infection. A painful red eye with light sensitivity and blurred vision is the combination that warrants urgent evaluation. Redness that comes and goes with a seasonal pattern is almost always allergic. Redness that appeared after an injury, no matter how minor, could involve a corneal scratch or foreign body.
Recurrent redness in one eye, particularly with light sensitivity, raises the possibility of uveitis and is worth investigating even if it resolves each time, since repeated episodes can cause cumulative damage inside the eye.