A red eye usually means the tiny blood vessels on the surface of your eye have swollen or dilated, making the white of your eye look pink or bloodshot. Most of the time the cause is minor, like dryness, irritation, or allergies, and it clears up on its own. But certain combinations of symptoms, particularly redness with pain, vision changes, or sensitivity to light, point to something more serious.
The Most Common Causes
The surface of your eye is covered in a clear membrane packed with tiny blood vessels. When something irritates or inflames that surface, those vessels expand and become visible. The triggers range from everyday annoyances to infections that need treatment.
Dry eyes are one of the most frequent culprits. When your tear film breaks down or you aren’t producing enough tears, the surface of your eye becomes irritated and inflamed. Long hours of screen time, air conditioning, wind, and aging all contribute. For mild or occasional dryness, over-the-counter artificial tears are typically enough. If you use drops more than four times a day, choose preservative-free versions, since the preservatives themselves can irritate your eyes over time. Warm compresses held over your closed eyelids for a few minutes daily can also help by loosening oils that keep your tear film stable.
Allergies cause redness along with intense itching and clear, watery discharge. If your eyes get red and itchy every spring, or whenever you’re around a cat, allergies are the likely explanation. Environmental irritants work differently. Dust, smoke, and chemical fumes trigger redness without the immune response of a true allergy. Swimming pools are a common source: chlorine in the water reacts with sweat, body oils, and urine to form compounds called chloramines, which irritate both your eyes and lungs. That strong “chlorine smell” at a pool is actually the smell of chloramines, not clean water.
Pink Eye: Viral, Bacterial, or Allergic
Conjunctivitis, commonly called pink eye, is an infection or inflammation of the clear tissue lining your eyelids and covering the white of your eye. The type you have determines what it feels like, how it looks, and how long it lasts.
Viral conjunctivitis feels gritty and sandy, like something is stuck in your eye. Your eyes may be moderately red with watery discharge and noticeably sensitive to light. There’s no medication that speeds it up. Like a cold, it has to run its course, which can take two to three weeks.
Bacterial conjunctivitis is the one with the dramatic yellow or green discharge. You may wake up with your eyelids crusted shut. The redness can look alarming, but bacterial pink eye usually causes less pain than the viral type. Antibiotic eye drops typically improve symptoms within three or four days, though you need to finish the full course to prevent it from coming back.
Allergic conjunctivitis produces mild redness with clear, watery discharge and sometimes severe itching. It isn’t contagious. It tends to flare seasonally or after exposure to a specific trigger like pet dander or pollen.
A Bright Red Patch on Your Eye
If you notice a vivid, blood-red spot on the white of your eye rather than overall pinkness, you’re likely looking at a subconjunctival hemorrhage. This happens when one of the tiny blood vessels under the clear membrane of your eye breaks and leaks a small amount of blood. It looks startling but is almost always harmless.
Common triggers include coughing, sneezing, straining, or anything that briefly spikes pressure in your veins. Sometimes it happens for no obvious reason at all. The spot doesn’t hurt and doesn’t affect your vision. Most subconjunctival hemorrhages clear up on their own within two weeks, shifting from bright red to yellow-brown as the blood is reabsorbed.
Contact Lens Risks
If you wear contact lenses and your eye is red, pay closer attention. Contact lenses sit directly on your cornea and can trap bacteria against it, especially when you sleep in them. Sleeping in lenses, even just a nap, increases your risk of a corneal infection six- to eightfold. About one third of contact lens wearers report sleeping or napping in their lenses, making this one of the most common and most dangerous habits.
A corneal ulcer is the serious end of this spectrum. It’s an open sore on the cornea caused by bacterial or other microbial infection. Symptoms include redness, pain, tearing, blurred vision, and sometimes a visible white spot on the cornea. CDC case reports have documented severe corneal ulcers, including corneal perforation, linked to sleeping in lenses and using lenses purchased without a valid prescription. If you wear contacts and develop a red, painful eye, remove your lenses immediately and get seen by an eye care provider the same day.
Deeper Inflammation: Uveitis
Not all eye redness comes from the surface. Uveitis is inflammation of the middle layer of your eye, and it can cause a deep, aching redness that looks different from typical pink eye. The redness often concentrates in a ring around the colored part of your eye (the iris) rather than spreading evenly across the white.
What makes uveitis worth knowing about is that it’s sometimes a sign of something happening elsewhere in your body. Autoimmune and inflammatory conditions like inflammatory bowel disease, lupus, sarcoidosis, and several types of inflammatory arthritis (including ankylosing spondylitis and psoriatic arthritis) are linked to uveitis. A specific genetic marker called HLA-B27 raises the risk. Uveitis can also come from infections or have no identifiable cause. It typically causes pain, light sensitivity, and blurred vision along with redness, and it requires prescription treatment to prevent damage to your eyesight.
Acute Glaucoma
This is the rarest cause on this list but the most urgent. Acute angle-closure glaucoma happens when the drainage system inside your eye gets physically blocked, usually by a bulging iris. Fluid backs up, pressure inside the eye spikes, and the result is severe pain, a very red eye, blurred vision, halos around lights, and often nausea or vomiting. It comes on suddenly and gets worse over hours.
This is a medical emergency. Without treatment, the high pressure damages the optic nerve and can cause permanent vision loss. If you experience intense eye pain with nausea and vision changes, go to an emergency room.
When Redness Needs Urgent Attention
Redness on its own is rarely an emergency. What matters is what comes with it. Seek immediate care if your red eye is accompanied by any of the following:
- Severe pain that doesn’t improve with over-the-counter drops, or pain that steadily worsens over several hours
- Sudden vision loss or blurring, even if it seems to partially improve on its own
- Sensitivity to light paired with pain or blurred vision
- A sudden shower of new floaters or flashes of light, especially with a shadow creeping across your field of vision
- Nausea or vomiting along with eye pain
- Chemical exposure from a household cleaner, industrial product, or any irritant splashing into your eye
- A puncture or penetrating injury from a sharp object (do not try to remove it or press on the eye)
For mild redness without pain or vision changes, simple measures often help: artificial tears for dryness, cool compresses for irritation, and avoiding whatever triggered it (allergens, smoke, chlorinated pools, or overworn contact lenses). If redness persists for more than a few days without improving, or keeps coming back, it’s worth having an eye care provider take a closer look to rule out causes you can’t see on your own.