What Is Conjunctivitis (Pink Eye)?

"Pink eye" sounds like one illness, but it's really three different problems sharing a nickname. Conjunctivitis means the conjunctiva — the clear membrane that lines the inside of your eyelids and covers the white of the eye — has become inflamed. That inflammation is what turns the white of the eye pink or red. What differs is the trigger, and the trigger changes how the condition behaves, how it spreads, and what tends to help.

The short video at the top of this page, "Conjunctivitis" (just over three minutes), walks through that basic definition — an inflammation or infection of the conjunctiva, in which the small blood vessels in the membrane become more visible and the eye takes on its pink colour.

Three triggers, three patterns

Viral conjunctivitis is the form that travels. It often starts in one eye and moves to the other within a few days, the discharge tends to be watery rather than thick, and it frequently arrives alongside a cold or a sore throat. Because it's caused by a virus, it generally has to run its course while the eye is kept comfortable and clean.

Bacterial conjunctivitis is the stickier version. The discharge is usually thicker and yellow-green, which is why eyelids can feel glued together first thing in the morning. It can affect one eye or both, and it's the form where a clinician is most likely to discuss medicated drops as part of the plan.

Allergic conjunctivitis doesn't spread at all — nobody catches it from you. Both eyes are usually involved at the same time, itching is the standout symptom, and it tends to flare alongside hay-fever-style sneezing or in response to triggers like pollen, dust or pet dander. If your eyes itch more than they hurt and both went pink together during pollen season, allergy belongs on the list of suspects.

How the infectious forms move around

The viral and bacterial forms pass mainly via hands: touching a watery or sticky eye, then touching a door handle, a towel or another person's hand. That's why pink eye moves so efficiently through households, classrooms and offices. Washing hands often, not sharing towels, pillowcases or eye makeup, and resisting the urge to rub your eyes won't end an episode overnight, but they make you much less likely to pass it on — or to move it from one of your own eyes to the other.

Contact lens wearers get one extra rule: stop wearing the lenses until the eye has settled and a clinician says it's fine to restart, and follow their advice about lenses and cases that were in use during the infection.

Not every red eye is pink eye

It's worth knowing that conjunctivitis is only one entry on the list of red-eye causes. A second video on this site, "Red Eyes", makes exactly that point: redness is commonly down to allergy, eye fatigue, over-wearing contact lenses or infections like pink eye — but it can sometimes signal something more serious. Eye pain rather than simple grittiness, sensitivity to light, blurred vision, or redness that follows an injury or chemical splash are all reasons to get checked promptly rather than assume it's ordinary pink eye. The same applies if a newborn baby has a red, sticky eye.

If an eye problem does need a specialist look, the examination is surface-level and unhurried — and if misalignment rather than redness is the concern, our guide to what strabismus (crossed eyes) is explains how alignment is assessed.

Frequently Asked Questions

How can you tell viral from bacterial pink eye? The pattern is a clue, not a proof: viral cases tend to be watery and travel from one eye to the other alongside cold symptoms, while bacterial cases produce thicker, yellow-green discharge that can stick the lids together overnight. A clinician can usually tell them apart by examining the eye.

Is pink eye always contagious? Only the infectious forms are. Viral and bacterial conjunctivitis can spread through hand-to-eye contact and shared towels or makeup; allergic conjunctivitis is a reaction, not an infection, and cannot be caught.

How long does conjunctivitis last? It varies with the cause. Many mild cases settle over days to a couple of weeks as the inflammation calms. If redness is getting worse rather than better, or vision changes, it should be checked instead of waited out.

Can I wear contact lenses with pink eye? Not until the eye has settled. Lenses can trap irritants and microbes against an already inflamed eye, so switch to glasses during an episode and ask your clinician when it's safe to restart and whether the old lenses and case should be replaced.

When is a red eye an emergency? Eye pain, light sensitivity, blurred or reduced vision, a red eye after an injury or chemical exposure, or redness in a newborn baby all warrant prompt, same-day assessment rather than home watching.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about conjunctivitis, not medical advice and not a diagnosis. Eye pain, light sensitivity, changes in vision, or a red eye in a newborn should be assessed promptly by a clinician.