Pink eye can be either viral or bacterial, and it can also be caused by allergies or irritants. Among infectious cases, viral conjunctivitis is the more common culprit in adults, while bacterial cases account for a smaller share than most people assume. One large study of over 3,000 children diagnosed with conjunctivitis found that 40% of cases were viral and only 10% were confirmed bacterial, with the rest classified as allergic or unspecified. Despite this, antibiotics are prescribed in more than half of pediatric cases, suggesting widespread overtreatment.
The distinction matters because the two types feel different, spread differently, and respond to different treatments. Here’s how to tell them apart and what to expect from each.
What Causes Each Type
Viral pink eye is most often caused by adenovirus, the same family of viruses behind many common colds. It can also be triggered by herpes simplex virus or the varicella-zoster virus (the one responsible for chickenpox and shingles). You can catch it the same way you catch a cold: touching contaminated surfaces, shaking hands, or being near someone who coughs or sneezes.
Bacterial pink eye is caused by various bacteria. It tends to show up in environments where people are in close physical contact, particularly daycares and schools. In rare but serious cases, sexually transmitted bacteria can cause a severe form called hyperacute conjunctivitis, which produces intense swelling, pain, and heavy discharge and requires prompt treatment.
How the Symptoms Differ
The biggest clue is the type of discharge your eye produces. Viral pink eye causes a watery, clear discharge. Your eye will look red and may feel gritty, almost like something is stuck in it. Some people also notice sensitivity to light. It often starts in one eye and spreads to the other within a day or two.
Bacterial pink eye produces a thicker, yellowish or greenish discharge. This is the type that glues your eyelids shut overnight, making it hard to open your eyes in the morning. Burning and irritation are common, along with mild eyelid swelling. It can also start in one eye and spread to the other, but it doesn’t always.
One physical sign that helps distinguish the two: viral pink eye often causes a small, tender, swollen lymph node just in front of the ear on the affected side. You can sometimes feel it by pressing gently in front of your earlobe. This swollen node is rare in typical bacterial conjunctivitis.
How Quickly Symptoms Appear
The timeline from exposure to symptoms varies between the two types. Bacterial conjunctivitis moves fast, with symptoms typically appearing 24 to 72 hours after exposure. Viral conjunctivitis has a wider window. Symptoms can show up anywhere from 12 hours to 12 days after infection, which makes it harder to trace back to a specific contact.
How Long It Lasts and Spreads
Both types are contagious for as long as the eye is tearing and producing discharge. For most people, symptoms improve within a few days to two weeks regardless of the cause. Viral pink eye tends to be contagious for 10 to 14 days from the time symptoms begin, which is longer than many people expect.
During that window, basic hygiene makes a real difference. Wash your hands frequently, use a separate towel and pillowcase, and avoid touching your face. For kids in school or daycare, the general guidance is that they can return once they no longer have a fever, can keep their hands clean, and can avoid close contact with other children. Kids who can’t reliably do those things should stay home until symptoms clear.
Treatment for Each Type
Viral pink eye has no specific treatment. Antibiotics do nothing against viruses, and using them unnecessarily contributes to antibiotic resistance. The infection runs its course on its own. Cool compresses and artificial tears can help with comfort in the meantime.
Mild bacterial pink eye is also likely to resolve without treatment. The American Academy of Ophthalmology notes that mild bacterial cases are generally self-limited, meaning your immune system clears the infection on its own. Antibiotic eye drops can shorten the duration and reduce how contagious you are, so they’re sometimes prescribed for convenience or in settings like daycares where spread is a concern. For severe bacterial infections, particularly the hyperacute form that causes heavy pus, significant swelling, and pain, antibiotics are essential and treatment should start quickly.
The key takeaway from current guidelines: indiscriminate use of antibiotic drops should be avoided. If your symptoms are mild and your discharge is watery, antibiotics almost certainly won’t help.
Allergic Pink Eye Looks Different
If both eyes are itchy and watery but you don’t have thick discharge or crusty eyelids, allergies are a more likely cause than infection. Allergic conjunctivitis typically comes with other allergy symptoms like sneezing or a runny nose, and it isn’t contagious. Over-the-counter antihistamine eye drops usually provide relief.
Symptoms That Need Prompt Attention
Most pink eye is a nuisance, not a danger. But certain symptoms suggest something more serious is going on. Eye pain (not just irritation), sensitivity to light, blurred vision, or intense redness that doesn’t match typical pink eye can indicate conditions that affect deeper structures of the eye. These warrant a same-day visit to a healthcare provider or eye doctor rather than a wait-and-see approach.