Conjunctivitis can be either viral or bacterial, but viral cases are far more common. Roughly 80% of acute infectious conjunctivitis is caused by viruses, making it the dominant form in adults. Bacterial conjunctivitis shows up more often in infants, school-age children, and older adults. Both types cause red, irritated eyes, but they differ in symptoms, how long they last, and how they’re treated.
How to Tell the Difference
The discharge from your eye is the most reliable clue. Viral conjunctivitis typically produces a watery, clear discharge. In diagnostic studies, watery discharge had a 77% sensitivity for identifying viral cases, and its presence made a bacterial cause far less likely. Viral pink eye also tends to start in one eye and spread to the other within a day or two, and it often accompanies or follows a cold, sore throat, or upper respiratory infection.
Bacterial conjunctivitis produces thicker, yellow-green discharge that accumulates throughout the day. The hallmark sign is waking up with your eyelids stuck together. That single finding correctly identified bacterial cases 86% of the time in clinical studies. Bacterial cases can also start in one or both eyes, but the heavy, sticky discharge is what sets them apart.
Neither sign is foolproof on its own. Plenty of viral cases produce some crusting, and some bacterial infections start with watery eyes before the discharge thickens. But as a general rule: watery and thin points toward viral, thick and sticky points toward bacterial.
What Causes Each Type
Adenoviruses are responsible for the majority of viral conjunctivitis cases. These are the same viruses behind many common colds, which is why pink eye and cold symptoms so often travel together. Herpes simplex virus and varicella-zoster virus (the chickenpox/shingles virus) can also cause viral conjunctivitis, though less commonly. Enterovirus is another occasional culprit.
The bacteria involved depend on the patient’s age. In children, the usual suspects are Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis. In adults, Staphylococcus aureus is the most common cause, particularly in chronic cases that linger for weeks. Chlamydia can also cause conjunctivitis in sexually active adults and in newborns exposed during delivery. A rare but serious form, hyperacute bacterial conjunctivitis, is caused by gonorrhea-related bacteria and requires urgent treatment.
Recovery Time
Viral conjunctivitis clears up on its own in 7 to 14 days for most people, though stubborn cases can take two to three weeks. There’s no medication that speeds this up. Antibiotics do nothing against viruses, and the American Academy of Ophthalmology specifically warns against prescribing them for viral cases.
Bacterial conjunctivitis also resolves without treatment in many mild cases, typically improving within 2 to 5 days, though it can take up to two weeks to fully clear. Antibiotic eye drops can shorten that timeline, reduce the risk of complications, and help you become less contagious faster. But for mild bacterial cases, a “wait and see” approach is reasonable. The AAO notes that mild bacterial conjunctivitis is likely to be self-limited, and indiscriminate antibiotic use should be avoided.
How It Spreads
Both viral and bacterial conjunctivitis are highly contagious. The infection spreads through direct contact with eye discharge, contaminated hands, shared towels, pillowcases, or makeup. Viral conjunctivitis is especially easy to catch because the same viruses spread through coughs and sneezes.
You remain contagious as long as your eyes are tearing and producing discharge. For bacterial cases treated with antibiotics, the contagious window shortens significantly. Children can generally return to school once they no longer have a fever, can keep their hands clean, and can avoid close contact with others. Children who can’t reliably practice good hygiene should stay home until symptoms clear.
Basic prevention comes down to hand hygiene. Wash your hands frequently, avoid touching your eyes, don’t share towels or eye cosmetics, and replace contact lens cases regularly.
Allergic Conjunctivitis Is a Third Possibility
Not all pink eye is infectious. Allergic conjunctivitis causes red, itchy, watery eyes but isn’t contagious at all. The giveaway is intense itching in both eyes simultaneously, often alongside sneezing, a runny nose, or other allergy symptoms. Seasonal patterns (worse in spring or fall) are another strong hint. If your eyes are itchy but you don’t have thick discharge or cold symptoms, allergies are the more likely explanation.
Symptoms That Need Prompt Attention
Most conjunctivitis is uncomfortable but harmless. A small number of cases, however, involve the cornea (the clear front surface of the eye), a condition called keratitis. This is more common with certain viral strains and can develop one to two weeks after conjunctivitis symptoms first appear.
The warning signs that suggest something more serious than routine pink eye include significant eye pain (not just irritation), blurred or decreased vision, intense sensitivity to light, and a feeling that something is lodged in your eye that won’t go away. These symptoms can signal corneal involvement or other complications that, left untreated, can affect your vision permanently. Herpes-related conjunctivitis, in particular, can produce characteristic corneal damage that requires specific antiviral treatment.
If your pink eye hasn’t started improving after a week, if symptoms are getting worse rather than better, or if you develop any of the warning signs above, an eye specialist can determine what’s going on and whether you need targeted treatment.