Viral vs bacterial pink eye: how to tell them apart

Viral and bacterial pink eye can look alike, but a few clues help. Viral pink eye usually brings watery discharge and a gritty or burning feeling, often arrives with a cold, and tends to start in one eye and reach the other within a few days. It spreads easily, and antibiotic drops do nothing for it. Bacterial pink eye is more likely to produce thick yellow or green discharge that glues the lashes together by morning. Allergic pink eye itches, usually affects both eyes, and is not contagious at all.

In a house with a primary-school child, a pink eye at breakfast brings the same three questions: is it catching, can they go to school, and do we need drops? The clues above are tendencies, not rules, and even doctors can't always tell from the outside. What a parent can do is notice them, stop the infection going around the house, and know the signs that mean a red eye is not simple pink eye.

Four kinds of pink eye, side by side

Pink eye is the everyday name for conjunctivitis, an inflammation of the conjunctiva, the thin, clear layer covering the white of the eye and the inside of the eyelids. When its tiny blood vessels swell, the white turns pink or red. Viruses, bacteria, allergies and irritants can all set it off.

Itch is the most useful single clue. Allergy itches; infections tend to feel gritty, sore or burning, though they can itch a little too. Allergic pink eye has its own column, itchy eyes in allergy season, with habits that keep pollen away from the eyes.

Irritant pink eye usually settles once the eyes are rinsed with clean water and the cause is gone, after a smoky bonfire, say, or a long afternoon in a chlorinated pool. A chemical splash is a different matter: rinse with plenty of clean water for at least 15 minutes and get urgent care, as set out in eye emergencies and first aid.

Viral pink eye: the one that goes around

Viruses cause most infectious pink eye. Often they are the same viruses behind a common cold, so the eye trouble comes with a runny nose, a cough or a sore throat, and it travels through classrooms, daycare rooms and households with ease.

Typical signs are pink or red whites, plenty of watery discharge, a sandy or burning feeling, puffy lids and some discomfort in bright light. It commonly starts in one eye and reaches the other a few days later, often because a hand rubs one eye and then the other. Some people also get a small, tender swelling just in front of the ear, which is a lymph node reacting to the infection.

Viral pink eye usually gets better on its own, typically over one to two weeks and sometimes longer, and it can feel worse for the first few days before it improves. Antibiotics don't work against viruses, so care is about comfort and about not passing it on. A cool, clean, damp cloth over closed lids can feel soothing. Some viral types are especially contagious, and a few can also inflame the cornea, the clear front window of the eye, leaving vision hazy or light uncomfortable for a while. That is one reason to have a child's pink eye looked at rather than waiting it out.

Bacterial pink eye: the sticky one

Bacteria cause fewer cases overall, though bacterial pink eye is seen more often in children than in adults. The giveaway is the discharge: thicker, yellow, green or creamy, building up along the lashes and gluing the lids shut after sleep. It can affect one eye or both, and the cold-like symptoms of viral pink eye are often missing. Young children sometimes have it at the same time as an ear infection.

Mild bacterial pink eye often clears up on its own, and antibiotic drops or ointment can shorten some cases. Whether they are needed is for the doctor to decide.

A crusty morning alone doesn't prove bacteria, though, since dried tears and mucus collect overnight in viral and allergic pink eye too. Doctors look at the whole picture.

To clean crusts at home, wet a clean cotton pad or washcloth with warm (not hot) water and wipe gently from the inner corner outward. Use a fresh pad for each wipe and each eye, throw it away, and wash your hands afterward.

What the doctor looks for

Depending on where you live, a simple pink eye may first be seen by your family doctor, a pediatrician or an eye doctor. An eye doctor, meaning an ophthalmologist or, in many places, an optometrist, is the right person when the eye hurts, vision changes, you wear contact lenses, or it isn't getting better. Finding an eye doctor and planning a visit and who to ask about an eye worry help you work out the first stop.

The doctor will usually ask when it started, which eye came first, whether it itches or hurts, what the discharge looks like, who else has it, and whether you wear contact lenses. Then they check the sight in each eye, look at the lids and the inside of the lower lid, and feel for that swollen node in front of the ear. An eye doctor uses a microscope with a bright light and may put in a yellow-orange dye that shows scratches or sores on the cornea under a blue light. A swab of the discharge is sometimes taken when the infection is severe, keeps coming back, isn't improving, or affects a newborn.

Antibiotics help only bacterial pink eye. They do nothing for viral or allergic cases, and using them when they aren't needed brings side effects without benefit and adds to the wider problem of antibiotic resistance. Allergic pink eye is managed in other ways, and your eye doctor or pharmacist can advise what suits.

Never reach for someone else's drops or a half-used bottle from last year. They may be the wrong kind, an opened bottle can become contaminated, and some prescription drops can make certain eye infections much worse. If the eyes look worst first thing in the morning, a photo taken then can help the doctor.

Keeping it from spreading at home and school

Viral and bacterial pink eye spread through hands, towels, pillowcases and anything else that touches the eyes. A few habits make a real difference:

• Wash hands with soap and water often, especially after touching the eyes, wiping away discharge or putting in drops. Help small children do it properly.
• Give everyone their own towel and washcloth, change the pillowcase of the person with pink eye often, and wash these in hot water.
• Don't share eye makeup, makeup brushes, eye drops, glasses or sunglasses, and throw away eye makeup used while the eye was infected.
• Stop wearing contact lenses until an eye doctor says it's fine, and ask whether the lenses and case you were using should be replaced. Glasses do the job meanwhile.
• Wipe the things everyone touches: door handles, light switches, tablets, game controllers.
• Skip swimming lessons until it has cleared, both for your child's eyes and for the other swimmers.

With Halloween a few days away, the same goes for costume lenses and face paint near the eyes: never share them, and leave them out while anyone in the house has pink eye. Colored contact lenses for Halloween explains why costume lenses need a proper fitting even for healthy eyes.

School and daycare rules vary a lot. Some ask children to stay home until a doctor has seen them, or until the discharge has stopped. Others let a child with mild pink eye attend as long as they feel well, and some health services don't advise keeping children home for pink eye alone. In Japan, where I live, certain highly contagious viral types mean a child stays home until a doctor says they can return. Check your own school's policy, and ask the doctor when your child is unlikely to pass it on. Adults in childcare or healthcare jobs may have workplace rules too.

When a red eye is not simple pink eye

Simple pink eye is uncomfortable but usually mild. Vision stays normal, and the eye feels gritty rather than truly painful. These signs point to something else and mean seeing an eye doctor today:

• real pain in the eye, not just grittiness
• light that hurts to look at
• blurred vision that doesn't clear when your child blinks or the discharge is wiped away
• a red eye in a contact lens wearer: take the lenses out now, keep them and the case, and get same-day care, because it may be an infection of the cornea, which needs quick treatment
• a baby in the first month of life with red eyes, swollen lids or discharge
• an injury, something in the eye, or a chemical splash
• red, swollen, tender eyelids and skin around the eye, especially with a fever or a child who seems unwell
• blisters or a rash on the eyelids, forehead or tip of the nose
• symptoms that are getting worse after a few days instead of better

Babies often have watery eyes and a little sticky discharge from a blocked tear duct, which is common, but a red eye in a newborn always needs a doctor the same day.

Some red eyes are emergencies. A very red, painful eye with blurred vision, halos around lights, headache and nausea or vomiting can be acute angle-closure glaucoma. Sudden loss of vision in one eye, even if it comes back, can be a warning sign of stroke. For these, go to an emergency department now or call your local emergency number (such as 911, 999, 112, or 119 in Japan). Chemical splashes, objects stuck in the eye and hard blows are covered step by step in eye emergencies and first aid.

Questions people ask

How long is pink eye contagious?

It depends on the cause. Treat viral and bacterial pink eye as catching while the eye is red and producing discharge, and keep up the hand washing and separate towels until it has settled. Allergic pink eye never spreads. Your doctor can tell you when your child is unlikely to pass it on, and your school may have its own rule.

Is it pink eye or a stye?

A stye is a tender, red lump on the edge of an eyelid, and the white of the eye usually stays white. Pink eye turns the white of the eye pink or red, usually without a lump. If you are unsure, or the swelling spreads across the lid, see a doctor.

Sources

• American Academy of Ophthalmology: eye health
• NHS conditions