Pink eye almost always traces back to one of three things: a virus, bacteria, or an allergen that reached the surface of your eye. The most likely route? Your own hands. Touching a contaminated surface, then rubbing or touching your eye, is the single most common way the infection gets in. But there are several other paths worth knowing about, because understanding which one caused yours helps you figure out how long it will last and whether you can spread it.
Viruses Are the Most Common Cause
About 90% of viral pink eye cases come from adenoviruses, the same family of viruses responsible for the common cold. If you’ve had a cold, sore throat, or upper respiratory infection in the past week or two, that’s likely your answer. The virus traveled from your nose or throat to your eye, usually on your fingers. Viral conjunctivitis can show up anywhere from 12 hours to 12 days after exposure, so you may not connect it to the cold you had last week.
COVID-19 can also cause conjunctivitis, typically alongside respiratory symptoms. Herpes simplex virus accounts for a small percentage of cases (roughly 1 to 5%), and varicella-zoster, the virus behind chickenpox and shingles, can reach the eye through direct contact with skin lesions or by inhaling airborne particles.
Bacterial Pink Eye and How It Differs
Bacterial conjunctivitis tends to produce thicker, yellowish or greenish discharge that can crust your eyelids shut overnight. In adults, it’s commonly caused by staph bacteria. In children, the usual culprits are different species that also live in the nose and throat. Symptoms typically appear 24 to 72 hours after exposure, a tighter window than the viral form.
Bacteria reach the eye the same way viruses do: contaminated hands, shared towels, pillowcases, or makeup. One less obvious route involves sexually transmitted infections. Chlamydia and gonorrhea can both cause pink eye in adults through hand-to-eye transfer of genital secretions. Chlamydia-related conjunctivitis is often one-sided and tends to be chronic if untreated.
The Hands-to-Eyes Problem
The CDC points to a simple chain of events behind most cases: you touch a surface carrying the virus or bacteria, then touch your eye before washing your hands. Doorknobs, phones, shared keyboards, and countertops can all harbor these germs. Adenoviruses in particular are hardy and survive on surfaces for extended periods.
If someone in your household or workplace has pink eye, shared objects are the most likely bridge. Towels, pillows, eye drops, and cosmetics are common vehicles. The infection can also spread through a handshake followed by an eye rub, which is why outbreaks move quickly through schools and daycare centers.
Swimming Pools Are a Surprisingly Common Source
If your pink eye showed up after swimming, the pool itself may be the cause, and not necessarily from an infection. Chlorine reacts with sweat, urine, and skin cells in the water to form chemical byproducts called chloramines. These irritants are responsible for that familiar “pool eye” sting and can cause genuine conjunctivitis. One CDC analysis found that 33 to 42% of reported pool-related health complaints involved eye problems tied to pool chemicals.
But pools also harbor viruses. Adenoviruses can survive in inadequately treated water and cause outbreaks of conjunctivitis among swimmers. The virus enters the water through fecal contamination and can infect the eyes directly. Wearing swim goggles and avoiding pools with a strong chemical smell (a sign of high chloramine levels, not cleanliness) reduces the risk.
Allergies and Irritants
Not all pink eye is contagious. If both eyes are itchy and watery but you don’t have thick discharge or cold symptoms, allergies are the most likely explanation. Seasonal allergic conjunctivitis flares in spring and summer from pollen and grass. The year-round form is triggered by pet dander, dust mites, and mold spores indoors. Unlike infectious pink eye, the allergic type won’t spread to anyone else, and it tends to come with sneezing or nasal congestion.
Chemical irritants can also inflame the eye’s surface. Fumes, smoke, chlorine, household cleaners, and even certain eye drops can trigger a reaction that looks and feels like pink eye but resolves once you remove the irritant.
Contact Lenses Raise the Risk
If you wear contacts, they deserve a hard look. Wearing lenses too long, sleeping in them, rinsing them with tap water, or reusing old solution all create conditions where bacteria, fungi, and even parasites can get trapped against the surface of your eye. The lens acts like a barrier that holds germs in place and limits the natural flushing action of your tears. Poor lens hygiene is one of the most preventable risk factors for eye infections.
How to Tell Which Type You Have
The type of discharge gives you the strongest clue. Viral pink eye produces a thin, watery discharge and often starts in one eye before spreading to the other within a day or two. It frequently accompanies cold symptoms. Bacterial pink eye produces thicker, colored discharge and can start in either or both eyes. Allergic conjunctivitis makes both eyes intensely itchy with clear, watery tearing.
Viral and bacterial forms are both contagious for as long as symptoms are present. There’s no single defined safe-return date. General guidance from the CDC is to stay home if you can’t avoid close contact with others, especially if you have fever or other systemic symptoms. Bacterial pink eye typically becomes less contagious within 24 to 48 hours of starting antibiotic drops, while viral pink eye has no antibiotic treatment and can remain contagious for up to two weeks.
Stopping the Spread From Here
Whatever caused your pink eye, the same habits prevent you from passing it along or reinfecting yourself. Wash your hands frequently, especially after touching your face. Replace your pillowcase daily. Throw away any eye makeup you used while symptomatic. If you wear contacts, switch to glasses until the infection fully clears and start with a fresh pair of lenses and a new case afterward. Avoid sharing towels, and try not to touch or rub the infected eye, even when it itches.