Pink eye in kids is most often caused by a virus, but bacteria, allergies, and irritants can all trigger it too. The cause matters because it determines whether your child needs treatment, how long they’re contagious, and when they can go back to school or daycare.
Viral Infections: The Most Common Cause
Viruses are responsible for the majority of pink eye cases in children. Adenoviruses are the main culprit, though other respiratory viruses can cause it as well. These are the same types of viruses that cause colds, which is why pink eye often shows up alongside a runny nose or sore throat.
Viral pink eye typically starts in one eye and spreads to the other within a day or two. The discharge tends to be watery or clear rather than thick. Your child may complain of a gritty feeling, and you might notice their eyes look red and slightly swollen. Some kids develop sensitivity to light, though that’s less common. A telltale sign is swollen lymph nodes just in front of the ear.
Kids pick up the virus through close contact with an infected person, touching contaminated surfaces and then rubbing their eyes, or even swimming in pools that aren’t properly chlorinated. There’s no antibiotic for viral pink eye. It clears on its own, usually within one to two weeks. Cool compresses and artificial tears can help with comfort in the meantime.
Bacterial Pink Eye
Bacterial conjunctivitis is the second most common infectious cause in children. Three bacteria are responsible for most cases: Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis. These spread the same ways as the viral form, through direct contact, shared towels, or contaminated hands.
The hallmark of bacterial pink eye is thick, yellowish or greenish discharge. The single best predictor is waking up with both eyes crusted or “glued” shut. Kids often have red, puffy eyelids and describe a stinging or burning sensation. Unlike viral cases, bacterial pink eye frequently affects both eyes from the start.
This form does respond to antibiotic eye drops or ointment. Once treatment begins, the contagious period ends quickly, and most children see improvement within 24 to 48 hours.
Allergic Conjunctivitis
Not all pink eye is an infection. Allergies are a common non-infectious cause, especially during spring and fall when pollen counts are high. Dust mites, pet dander, and mold can trigger it year-round.
Allergic pink eye looks and feels different from the infectious types. The most distinctive feature is intense itching, often in both eyes at once. The discharge is watery or stringy rather than thick. You might also notice swelling of the clear tissue covering the white of the eye, which can look puffy or almost gel-like. There’s no fever, no crusting in the morning, and your child isn’t contagious.
Because there’s no cure for the allergic form, the most effective approach is avoiding whatever triggers it. Over-the-counter allergy eye drops and cool compresses can reduce symptoms. If your child gets allergic pink eye repeatedly, identifying and minimizing exposure to the specific allergen makes the biggest difference.
Irritants and Chemical Exposure
Chlorine from swimming pools, smoke, shampoo, or even dirt and sand can irritate a child’s eyes enough to cause redness and tearing that looks like pink eye. This type typically resolves on its own once the irritant is removed. Gently flushing the eye with clean water or saline speeds up recovery. If redness and discomfort persist beyond a day after the exposure, the irritation may have opened the door to an actual infection.
Causes Specific to Newborns
Newborns can develop pink eye for reasons that don’t apply to older children. A blocked tear duct is one of the most common causes in the first few months. The duct that normally drains tears from the eye into the nose hasn’t fully opened yet, leading to watery, sometimes crusty eyes. A gentle warm massage between the inner corner of the eye and the nose often helps. If it doesn’t resolve by the baby’s first birthday, a minor surgical procedure may be needed.
Babies can also develop pink eye from infections passed during childbirth. A mother with untreated chlamydia can transmit bacteria to the baby’s eyes, with symptoms appearing 5 to 12 days after birth: redness, swollen lids, and pus. Gonorrhea can cause a more aggressive form that appears within the first 2 to 5 days of life and, if untreated, can lead to serious complications including bloodstream infections. Herpes virus can also be transmitted during delivery, though this is rarer.
Hospitals routinely apply antibiotic ointment to newborns’ eyes shortly after birth to prevent these infections. That ointment itself can cause mild redness and swelling, but this chemical irritation is harmless and clears within 24 to 36 hours. Any pink eye symptoms in a newborn beyond that window should be evaluated promptly.
How to Tell Which Type Your Child Has
The discharge is your best clue. Watery, clear discharge points toward a virus or allergy. Thick, yellow-green pus that crusts the eyes shut overnight is the classic sign of a bacterial infection. Intense itching with both eyes affected, especially during allergy season, suggests an allergic cause.
Context matters too. If your child has a cold, viral pink eye is the most likely explanation. If they’ve been around another child diagnosed with bacterial conjunctivitis, that moves to the top of the list. If symptoms flare every spring or whenever they’re around a cat, allergies are the probable trigger.
How Long Kids Stay Contagious
For infectious forms, your child generally remains contagious as long as their eyes are tearing and matted. With bacterial pink eye, the contagious period ends once antibiotic treatment starts or symptoms clear up. With viral pink eye, your child stays contagious for as long as signs and symptoms are present, which can mean up to two weeks.
Most schools and daycares set their own return policies, but they generally follow this principle: a child with bacterial pink eye can return once they’ve started antibiotics, while a child with viral pink eye needs to wait until the tearing and redness have resolved. In practice, many schools don’t require children to stay home for mild cases, so it’s worth checking your specific school’s policy.
Signs That Need Prompt Attention
Most pink eye in kids is uncomfortable but not dangerous. However, certain symptoms suggest something more serious is going on. Watch for eye pain (not just irritation), blurred vision that doesn’t clear when you wipe away discharge, sensitivity to light, intense redness, or symptoms that keep getting worse instead of better. Children with weakened immune systems also need closer monitoring. If your child is on antibiotic drops and there’s no improvement after 24 hours, that’s another reason to follow up.