When your eyes turn red, the tiny blood vessels on the surface of the eye have expanded or become inflamed, making them visible through the thin, clear tissue covering the white of the eye. This can happen for dozens of reasons, from something as harmless as a sneeze to something as serious as a sudden spike in eye pressure. Most causes are temporary and resolve on their own, but knowing what’s behind the redness helps you figure out whether to wait it out or get help.
The Most Common Causes
Red eyes show up so often that it’s easy to dismiss them, but the underlying cause matters. The short list of everyday triggers includes dry eyes, allergies, pink eye (conjunctivitis), a burst blood vessel, a foreign object like dust or an eyelash, and irritation from contact lenses or eye drops. Less common but more serious causes include corneal ulcers, glaucoma, and inflammation of deeper eye structures like the middle tissue layer of the eye wall.
Most of the time, redness comes from surface-level irritation. Your eyes respond to irritants by flooding the area with blood flow, which is your body’s standard inflammation response. The redness itself isn’t the problem. It’s a signal that something is irritating or damaging the eye’s surface.
Pink Eye: Bacterial, Viral, and Allergic
Pink eye is probably the first thing people think of when they see red eyes, and the type you have determines what to expect. Viral pink eye produces a watery, thin discharge and often accompanies a cold or upper respiratory infection. Bacterial pink eye produces thick, pus-like discharge that can glue your eyelids shut overnight. Allergic pink eye causes tearing and swelling but typically no thick discharge, and it almost always affects both eyes along with itching.
Viral pink eye clears on its own, usually within one to two weeks. Bacterial pink eye often needs antibiotic drops. Allergic pink eye responds to removing the allergen and using antihistamine drops. The discharge is your best clue: watery means viral, thick and sticky means bacterial, and teary with intense itching means allergic.
Screen Time and Blinking
If your eyes are red by the end of the workday, your screen is a likely culprit. When you look at a digital device, your blink rate drops dramatically. In a relaxed, distance-viewing position, you blink about 16 times per minute. While using a tablet or computer, that drops to roughly 6 times per minute. The blinks you do make are often incomplete, meaning your eyelids don’t fully close.
Blinking spreads your tear film evenly across the eye’s surface. When you blink less often or less completely, the tear film breaks apart between blinks, leaving patches of exposed tissue that dry out and become irritated. One study found that almost 97% of computer users had poor tear film stability. The exposed surface triggers inflammation, and the eye compensates by dilating blood vessels, producing that familiar redness and gritty feeling by late afternoon.
The fix is straightforward: look away from the screen every 20 minutes, consciously blink a few times, and consider preservative-free artificial tears if the dryness is persistent. Positioning your screen slightly below eye level also helps, because looking downward narrows the opening between your eyelids and reduces how much tear film evaporates.
Contact Lens Overwear
Contact lenses sit directly on the cornea, which gets its oxygen from tears rather than from blood vessels. A fresh lens allows oxygen to pass through, but the longer a lens stays in, the more it dries out and blocks that supply. When the cornea is starved of oxygen, new blood vessels start growing across the white of the eye toward the cornea to compensate. That’s the bloodshot look that chronic lens overwearers develop.
The bigger risk is that oxygen deprivation erodes the corneal epithelium, the thin protective layer on the front of the cornea. This creates tiny open sores (corneal abrasions) where bacteria can enter. Infections that spread through these abrasions can scar the cornea, distort your vision, and in severe cases cause permanent vision loss. If you wear contacts and notice persistent redness, pain, or a feeling that something is stuck in your eye, take the lenses out and give your eyes a break.
Burst Blood Vessels
A subconjunctival hemorrhage looks alarming: a bright red patch on the white of the eye that can cover a large area. It happens when a tiny blood vessel breaks just beneath the surface. Common triggers include coughing, sneezing, vomiting, heavy lifting, or simply rubbing your eye too hard. Blood thinners and conditions like high blood pressure or diabetes make them more likely.
Despite the dramatic appearance, these are almost always harmless. The blood is trapped between tissue layers and can’t reach the inside of your eye. No treatment is needed. The red patch typically clears within a few weeks as the blood is reabsorbed, shifting from bright red to yellow-green before disappearing entirely, similar to a bruise on your skin.
Air Quality and Environmental Irritants
Pollution, cigarette smoke, chlorine, and dry air can all cause chronic eye redness. Particulate matter in polluted air damages the eye’s surface over time. Research on urban particulate exposure shows measurable increases in inflammatory markers on the eye’s surface within just two weeks, along with decreased tear volume and reduced tear film stability. The protective outer layer of the cornea thins with prolonged exposure, leaving the eye more vulnerable to further irritation and infection.
If you live in an area with poor air quality or work around dust, fumes, or chemical vapors, artificial tears can help wash irritants off the eye’s surface. Wraparound sunglasses or safety glasses provide a physical barrier that reduces exposure significantly.
Redness-Relieving Eye Drops and Rebound
Over-the-counter redness-relieving drops work by constricting the swollen blood vessels on the eye’s surface. Most contain a decongestant called tetrahydrozoline. The problem is what happens when they wear off: the blood vessels can dilate even more than before, making your eyes redder than they were originally. This rebound redness can worsen over time, creating a cycle where you need the drops more and more frequently just to keep your eyes looking normal.
Newer formulations with a different active ingredient carry a lower risk of rebound redness. But for everyday redness from dry eyes or screen strain, preservative-free artificial tears are a better choice because they address the actual problem (a compromised tear film) rather than just masking the visible symptom.
When Red Eyes Signal an Emergency
Most red eyes are a nuisance, not a crisis. But certain combinations of symptoms point to conditions that can permanently damage your vision if not treated within hours. Seek immediate care if your red eye comes with any of the following:
- Sudden vision changes, including blurriness, loss of part of your visual field, or seeing halos around lights
- Severe eye pain, especially with a headache, light sensitivity, or nausea and vomiting
- Chemical exposure or a penetrating injury to the eye
- Swelling in or around the eye, particularly with fever, which may indicate an infection of the tissue around the eye
- Inability to open your eye or keep it open
These symptoms can indicate acute glaucoma (a dangerous spike in eye pressure), a deep eye infection, or inflammation of internal eye structures. Acute glaucoma in particular can cause irreversible optic nerve damage within hours if the pressure isn’t relieved. The classic presentation is a red, painful eye with blurred vision, halos around lights, and nausea, often coming on suddenly in the evening.