Red eyes are most often a sign of something minor: allergies, dry eyes, or a bout of pink eye. The redness itself happens because tiny blood vessels on the surface of your eye dilate in response to irritation or inflammation, becoming visible through the thin, transparent tissue covering the white of your eye. In most cases, the cause resolves on its own or with simple treatment. But certain combinations of symptoms, particularly redness paired with pain, vision changes, or nausea, can signal something that needs urgent attention.
Why Eyes Turn Red
The white of your eye is covered by a clear membrane called the conjunctiva, which contains an extensive network of tiny blood vessels. Normally these vessels are so small you can’t see them. When something triggers inflammation or irritation, those vessels widen and fill with more blood, making the white of your eye look pink or red. This response can be set off by infection, physical irritation, allergens, dryness, or pressure changes inside the eye.
Allergies and Hay Fever
Seasonal allergies are one of the most common reasons for red, itchy eyes. Pollen, dust mites, pet dander, and mold spores trigger an immune response that inflames the conjunctiva. The hallmark of allergic conjunctivitis is itching, often intense, along with watery eyes and sometimes puffiness. People with hay fever, asthma, or eczema are especially prone to this type of eye redness. It tends to affect both eyes at once and comes back predictably with allergen exposure.
Pink Eye (Conjunctivitis)
Pink eye is an umbrella term for inflammation of the conjunctiva, and the cause determines what it looks and feels like. Viral conjunctivitis, the most common type, produces watery discharge and typically clears up in 7 to 14 days without treatment, though some cases take two to three weeks. It often starts in one eye and spreads to the other within a day or two.
Bacterial conjunctivitis tends to produce thicker, yellowish or greenish discharge. A telltale sign is waking up with your eyelids stuck together from dried pus. It can also cause swelling and mild pain. The overlap in symptoms between viral and bacterial forms can make it tricky to tell them apart without an exam, but the type and color of discharge is the most useful clue.
Dry Eyes and Screen Time
Dry eye is a surprisingly common culprit behind chronic or recurring redness. Your eyes depend on a stable layer of tears to stay lubricated and comfortable. When that layer breaks down, whether from aging, medications, dry indoor air, or simply not blinking enough, the surface of the eye becomes irritated and blood vessels dilate.
Screen use is a major contributor. When you’re focused on a screen, your blink rate drops to about a third of what it normally is, and you may not fully close your eyes with each blink. As little as two hours of continuous screen time per day increases your risk of digital eye strain, which includes redness, irritation, and a gritty feeling. The fix is straightforward: blink deliberately, take breaks, and keep the air around you from getting too dry.
Broken Blood Vessel
A subconjunctival hemorrhage looks alarming but is almost always harmless. It appears as a bright red patch on the white of your eye, caused by a tiny blood vessel bursting under the conjunctiva. Unlike inflammation, it doesn’t produce discharge, pain, or vision changes. You might not even notice it until you look in a mirror. Sneezing, coughing, straining, or rubbing your eyes too hard can trigger one. It typically resolves on its own within one to two weeks as your body reabsorbs the blood.
Contact Lens Complications
Contact lenses create a unique set of risks for eye redness. Wearing lenses too long or not cleaning them properly raises the chance of keratitis, an inflammation of the cornea that can range from mild irritation to a serious infection. Microbial keratitis, caused by bacteria, fungi, or parasites invading the cornea through a contact lens, is particularly dangerous and can lead to permanent vision loss or the need for a corneal transplant in severe cases.
Other lens-related problems include dry eyes from reduced oxygen reaching the cornea, giant papillary conjunctivitis (bumps forming under the eyelid from chronic irritation), corneal scratches, and even new blood vessels growing onto the cornea in response to prolonged oxygen deprivation. Redness that starts while wearing contacts, especially if accompanied by pain or light sensitivity, warrants removing the lenses immediately.
Serious Conditions That Cause Red Eyes
Most red eyes aren’t emergencies, but a few conditions that cause redness can threaten your vision if untreated.
Acute angle-closure glaucoma occurs when fluid pressure inside the eye spikes suddenly. It causes severe eye pain, redness, blurred vision, halos around lights, headache, and often nausea or vomiting. This is a medical emergency that requires treatment within hours to prevent permanent vision loss.
Uveitis is inflammation of the middle layer of the eye wall. It can cause redness, pain, light sensitivity, and blurred vision. Left untreated, it can lead to complications including glaucoma. Uveitis sometimes occurs alongside autoimmune conditions.
Corneal ulcers, often linked to contact lens misuse or untreated infections, appear as painful red eyes with discharge and a sensation that something is stuck in your eye. They require prompt treatment to prevent scarring that can permanently affect vision. Scleritis, inflammation of the white of the eye itself, causes deep, boring pain that can worsen with eye movement and is often associated with autoimmune diseases like rheumatoid arthritis.
Other Common Triggers
Several everyday situations can cause temporary redness that doesn’t point to a larger problem:
- Foreign objects: Dust, an eyelash, or a small particle trapped under the eyelid causes immediate redness and tearing as your eye tries to flush it out.
- Eye drop overuse: Older redness-relief drops (containing ingredients that target a mix of receptors in blood vessel walls) can cause rebound redness. When the drops wear off, blood vessels dilate even more than before, creating a cycle of dependence. Newer formulations that target a more specific receptor type are less likely to cause this rebound effect.
- Irritants: Chlorine, smoke, and chemical fumes can inflame the eye’s surface directly.
- Injury: Blunt trauma, scratches, or burns to the eye cause redness along with pain and sometimes vision changes.
When Red Eyes Signal an Emergency
Red eyes paired with certain other symptoms need immediate medical evaluation. Seek urgent care if your vision changes suddenly, you have severe eye pain with a headache, you feel nauseous or are vomiting alongside eye redness, light begins to hurt your eyes, you see halos or colored rings around lights, or you have swelling in or around the eye that prevents you from opening it. A chemical splash or embedded object also warrants emergency attention. These combinations can indicate acute glaucoma, a serious infection, or trauma that risks permanent damage without fast treatment.