Conjunctivitis is inflammation of the conjunctiva, the thin, clear membrane that covers the white of your eye and lines the inside of your eyelids. Most people know it as pink eye. It’s one of the most common eye conditions, and while it usually looks alarming, it rarely causes lasting damage to your vision. The three main causes are infections (viral or bacterial), allergies, and irritants.
What Happens Inside the Eye
The conjunctiva contains a dense network of tiny blood vessels that are normally almost invisible. When something irritates or infects this tissue, your body releases inflammatory molecules like histamine and cytokines. These cause the blood vessels to widen, which is why the white of your eye turns pink or red. Immune cells then flood into the tissue from the bloodstream to fight off whatever triggered the response.
That redness, the hallmark of pink eye, is essentially your immune system working. The discharge, tearing, and swelling that often come with it are byproducts of the same process.
Viral Conjunctivitis
Viral pink eye is the most common type. It’s usually caused by the same group of viruses (adenoviruses) responsible for the common cold, and it often shows up alongside a sore throat, runny nose, or upper respiratory infection. The telltale sign is a thin, watery, clear discharge. Your eyes may feel gritty or irritated, but the discomfort is generally mild.
Viral conjunctivitis is highly contagious for 10 to 14 days. You can spread it as long as your eyes are red and tearing. It typically starts in one eye and spreads to the other within a few days. There’s no antibiotic treatment for it because antibiotics don’t work against viruses. Most cases resolve on their own within one to three weeks.
Bacterial Conjunctivitis
Bacterial pink eye produces a noticeably different kind of discharge: thick, yellow or green, and sticky enough to glue your eyelids together overnight. You might wake up unable to open your eyes until you wash the crust away. The redness can be more dramatic than with viral infections, and your eyelids may become swollen and painful.
Mild bacterial conjunctivitis often clears up without antibiotics within a week or so. Antibiotic eye drops can speed recovery and reduce the window of contagiousness, which is why many doctors still prescribe them, especially for children in school or daycare settings. If your symptoms haven’t improved after about 10 days, it’s worth seeing an eye doctor.
Allergic Conjunctivitis
If your pink eye comes with intense itching, that’s the strongest clue it’s allergic rather than infectious. Allergic conjunctivitis happens when allergens like pollen, pet dander, or mold land on the conjunctiva and trigger an immune overreaction. Your body’s mast cells release histamine, which causes itching, burning, tearing, and swelling. The discharge tends to be clear and watery, similar to viral pink eye, but it almost always affects both eyes at the same time.
Seasonal allergic conjunctivitis, triggered mainly by tree and grass pollen, accounts for roughly 90% of allergic cases. Perennial allergic conjunctivitis lasts year-round and is usually driven by indoor triggers like dust mites, mold, or animal dander. Unlike infectious pink eye, the allergic form is not contagious at all. Over-the-counter antihistamine eye drops and cold compresses are the first line of relief.
How to Tell the Types Apart
No single symptom is a perfect identifier, but the combination of clues usually points in the right direction:
- Watery, clear discharge + cold symptoms: likely viral
- Thick, yellow-green discharge + crusty eyelids: likely bacterial
- Intense itching + both eyes + allergy season: likely allergic
Viral and bacterial types both tend to start in one eye and may spread to the other. Allergic conjunctivitis almost always hits both eyes simultaneously because both are exposed to the same allergen. Pain level matters too. Conjunctivitis of any type causes discomfort, but severe pain, sensitivity to light, or blurred vision that doesn’t clear with blinking are warning signs of something more serious, like inflammation deeper inside the eye or a problem with the cornea.
When It’s More Than Pink Eye
A red eye isn’t always conjunctivitis. Several more serious conditions can mimic it, and knowing the red flags helps you act quickly. Severe pain (especially pain that feels deep rather than on the surface), sudden vision changes, extreme light sensitivity, or a red eye accompanied by nausea and vomiting can signal conditions like inflammation inside the eye or a sudden spike in eye pressure. These need prompt evaluation by an eye doctor. A red eye that keeps coming back or doesn’t respond to treatment within about 10 days also warrants a closer look.
How It Spreads and How to Stop It
Viral and bacterial conjunctivitis spread through direct contact with infected eye secretions, contaminated hands, or shared personal items. The virus can survive on surfaces, which is why pink eye tears through households, classrooms, and offices so efficiently.
The most important thing you can do is wash your hands frequently with soap and warm water, especially after touching your eyes or face. Beyond handwashing:
- Wash pillowcases, towels, and washcloths in hot water and detergent. Wash your hands again after handling them.
- Don’t share towels, pillows, eye drops, contact lenses, or eye makeup with anyone.
- Throw away cotton balls or tissues after each use.
- If only one eye is infected, don’t use the same eye drop bottle for both eyes.
- Clean your eyeglasses without contaminating shared surfaces like hand towels.
Children with pink eye should stay home from school or daycare if they can’t avoid close contact with others. They can typically return once symptoms improve and any prescribed treatment has been started.
Comfort Measures at Home
Cool compresses (a clean, damp washcloth over closed eyes) can ease the burning and swelling of viral or allergic conjunctivitis. For bacterial types, a warm compress can help soften and loosen the sticky discharge on your eyelids. Artificial tears can soothe irritation and help flush allergens or debris from the eye surface. If you wear contact lenses, switch to glasses until the infection fully clears. Discard any disposable lenses you wore while infected, and disinfect or replace your lens case.
Pink Eye in Newborns
Conjunctivitis in newborns is a special case. Babies can pick up infections during delivery if the mother carries certain bacteria, including chlamydia or gonorrhea. Herpes viruses and other bacteria that normally live in the birth canal can also cause it. Because a newborn’s immune system is still developing, these infections can cause severe eye damage if untreated.
To prevent this, hospitals in most states are required to apply antibiotic eye drops or ointment (typically erythromycin) to a newborn’s eyes within two to three hours of birth. Ironically, those preventive drops can themselves cause mild chemical irritation and temporary redness, which usually resolves on its own within a day or two. A blocked tear duct is another common cause of watery, irritated eyes in newborns that can look like pink eye but isn’t an infection.