Bacterial conjunctivitis is an infection of the conjunctiva, the thin clear membrane that covers the white of your eye and lines the inside of your eyelids. It’s one of the most common forms of pink eye, caused by bacteria rather than a virus or allergens. The hallmark sign is a thick, yellowish or greenish discharge that can glue your eyelids shut overnight. Most cases clear up within a week or two, but antibiotic eye drops speed recovery and reduce the chance of spreading it to others.
What Causes It
Different bacteria tend to be responsible depending on your age. In adults, Staphylococcus species are the most common culprits, followed by Streptococcus pneumoniae and Haemophilus influenzae. In children, bacterial conjunctivitis is actually more common than the viral form and is mainly caused by Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis.
You can pick up these bacteria by touching your eyes with contaminated hands, sharing towels or pillowcases, or through close contact with someone who has the infection. Contact lens wearers face a higher risk because the lens can trap bacteria against the eye’s surface. Young children in daycare settings spread it easily because they touch their faces frequently and share toys.
How It Differs From Viral and Allergic Pink Eye
Not all pink eye is the same, and the type of discharge is the biggest clue. Bacterial conjunctivitis produces a thick, purulent (pus-like) or mucopurulent discharge, while viral conjunctivitis causes a watery, thinner discharge. Allergic conjunctivitis tends to be intensely itchy, something that’s usually absent with bacterial infections.
A 2003 study identified three findings that strongly predicted bacterial conjunctivitis: eyelids glued shut in the morning, no itching, and no previous history of conjunctivitis. A later study in children narrowed it further, finding that sticky eyelids on waking, visible mucoid or purulent discharge, crusting on the lashes, absence of a burning sensation, and lack of watery discharge all pointed toward a bacterial cause. These patterns can help distinguish bacterial from viral pink eye, though there’s enough overlap that a definitive diagnosis sometimes requires a lab culture.
Symptoms to Expect
The classic presentation is redness in one or both eyes combined with a thick discharge. The redness comes from dilated blood vessels in the conjunctiva responding to the infection. You’ll typically notice:
- Discharge: Yellow, green, or white, often accumulating in the corner of the eye and along the lash line
- Eyelid crusting: Lids stuck together when you wake up, sometimes requiring a warm washcloth to open
- Conjunctival redness: The white of the eye appears pink or red
- Mild discomfort: A gritty or sandy feeling, though not the intense itch of allergies
Bacterial conjunctivitis often starts in one eye and spreads to the other within a day or two. Vision may be slightly blurry from the discharge coating the eye’s surface, but it clears when you blink or wipe the discharge away. If your vision stays blurry after clearing the discharge, that’s a sign something more serious may be going on.
How It Spreads and How Long You’re Contagious
Bacterial conjunctivitis is contagious from the moment symptoms appear until about 48 hours after starting antibiotic treatment, according to the American Academy of Ophthalmology. During that window, avoid sharing towels, washcloths, pillowcases, or eye makeup. Wash your hands thoroughly after touching your eyes or applying drops.
Once you’ve been on antibiotics for two days, you can resume normal hygiene routines. The AAO recommends switching out pillowcases and towels at the 48-hour mark and then going back to your usual habits. Children can typically return to school or daycare after those first 48 hours on treatment, though individual schools may have their own policies.
Treatment With Antibiotic Drops
Most bacterial conjunctivitis is treated with antibiotic eye drops or ointment. A typical course involves applying drops every two to four hours while awake for the first two days, then reducing to four times a day for up to five more days. The total treatment period is usually about a week.
Many mild cases of bacterial conjunctivitis will resolve on their own within one to two weeks without any treatment. However, antibiotics offer real advantages: they shorten the duration of symptoms, reduce how contagious you are, and lower the risk of complications. For children, treatment is generally recommended because bacterial conjunctivitis is so common in that age group and spreads quickly in group settings.
While you’re recovering, warm compresses can help loosen the crusty discharge on your eyelids. Soak a clean washcloth in warm water and hold it gently against your closed eye for a few minutes. Use a fresh cloth for each eye to avoid cross-contamination.
Complications of Untreated Infections
The vast majority of bacterial conjunctivitis cases resolve without lasting damage, but neglecting treatment in more aggressive infections can lead to problems. The most serious risk is the infection spreading to the cornea, the clear dome over your iris and pupil. This is called keratitis, and it begins when bacteria penetrate a break in the cornea’s surface layer.
If keratitis progresses, it can develop into a corneal ulcer, which carries the risk of permanent scarring, vision loss, and in rare extreme cases, loss of the eye. Complications of untreated corneal ulcers include scarring, abnormal blood vessel growth into the cornea, perforation, and irregular astigmatism. These outcomes are uncommon with ordinary bacterial conjunctivitis but underscore why persistent or worsening symptoms deserve prompt attention.
Bacterial Conjunctivitis in Newborns
Newborns can develop a specific form of bacterial conjunctivitis called ophthalmia neonatorum, which requires urgent medical care. The two most concerning causes are Chlamydia trachomatis and Neisseria gonorrhoeae, both of which a baby can pick up during delivery.
Gonococcal conjunctivitis appears early, often within the first five days after birth, and progresses rapidly. Most affected newborns develop profuse purulent discharge and swelling of the eyelids, though some show only mild inflammation. Without treatment, corneal ulceration and scarring can develop quickly, sometimes even despite treatment, resulting in visual impairment. Up to 15% of infants with gonococcal conjunctivitis also develop bacterial colonization in the throat, which carries a risk of the infection spreading through the bloodstream.
Chlamydial conjunctivitis presents later, typically 5 to 14 days after birth. It often starts in one eye before becoming bilateral, with discharge that begins watery or blood-tinged and later turns mucoid. While symptoms can resolve on their own, untreated infection may persist for up to a year and can lead to corneal scarring. Between 10% and 20% of infected newborns go on to develop pneumonia, so treatment always involves oral antibiotics rather than just eye drops, to clear the bacteria from the throat and prevent lung infection.
Because of these risks, hospitals routinely screen for maternal infections during pregnancy and apply preventive treatments to newborns’ eyes shortly after delivery.