Conjunctivitis is inflammation of the conjunctiva, the thin transparent membrane that covers the white of your eye and lines the inside of your eyelids. You probably know it as pink eye. It’s one of the most common eye conditions, and while it usually looks alarming, most cases resolve on their own within one to two weeks.
What the Conjunctiva Does
The conjunctiva works like a combination of a raincoat and plastic wrap for your eye. It blocks irritants like allergens and dust from reaching vulnerable tissue underneath, and it seals in moisture. It also produces the mucus layer that forms part of your tears, working alongside your tear glands to keep the eye surface lubricated. When this membrane gets inflamed, blood vessels dilate and become more visible, which is what gives the eye that characteristic pink or red color.
Types and What Causes Them
Conjunctivitis falls into a few distinct categories, and the cause determines how it feels, how it spreads, and how it’s treated.
Viral Conjunctivitis
This is the most common form. It’s caused by the same types of viruses responsible for colds, and it often shows up alongside an upper respiratory infection. The discharge is typically watery rather than thick. The pain usually feels sandy or gritty, as if something is stuck in your eye, and you may notice moderate to severe sensitivity to light. It tends to start in one eye and can spread to the other within a day or two.
Bacterial Conjunctivitis
Bacterial cases produce the most dramatic-looking symptoms. The hallmark is a thick yellow or green discharge that can be heavy enough to crust your eyelashes together overnight. Redness is usually moderate, and there’s typically minimal pain despite the alarming appearance. If you wear contact lenses, bacterial conjunctivitis can be more severe, and there’s a risk of developing a corneal ulcer, which causes intense pain and light sensitivity.
Allergic Conjunctivitis
Pollen, pet dander, dust mites, and other allergens can trigger this form. It almost always affects both eyes at the same time, and the main symptoms are itching (sometimes intense), clear watery discharge, and mild redness with swollen, puffy eyelids. Unlike viral and bacterial forms, allergic conjunctivitis is not contagious.
Irritant Conjunctivitis
Chemicals, chlorine, smoke, or a foreign object in the eye can cause inflammation that looks similar to other types. The eyes typically water heavily, and there may be a mucus discharge. Symptoms usually improve once the irritant is removed or flushed out.
How to Tell Which Type You Have
The discharge is the most useful clue. Watery discharge points toward a viral infection or allergies. Thick, yellow-green pus that glues your eyelids shut overnight strongly suggests a bacterial cause. If both eyes are itchy and watery, especially during allergy season, allergic conjunctivitis is the likely culprit.
Pain also helps distinguish types. Viral conjunctivitis often has that gritty, sandy sensation along with light sensitivity. Bacterial conjunctivitis rarely hurts much. Allergic conjunctivitis itches more than it hurts. A comprehensive eye examination can confirm the diagnosis when it isn’t obvious from symptoms alone.
How Conjunctivitis Is Treated
Treatment depends entirely on the cause, and one of the most important things to know is that antibiotics don’t work for most cases of pink eye. Viral conjunctivitis will not respond to antibiotics at all, and even mild bacterial conjunctivitis is likely to clear on its own. The American Academy of Ophthalmology cautions against the indiscriminate use of antibiotic drops or steroid drops, and no single antibiotic has been shown to work better than any other when they are prescribed.
Viral Cases
There’s no medication that speeds up a viral infection. It runs its course over one to two weeks. Cold compresses and artificial tears can relieve some of the inflammation and dryness while you wait. Focus on comfort measures and keeping the eye clean.
Bacterial Cases
Almost all cases of acute bacterial conjunctivitis are self-limited and will clear within about 10 days without treatment. When antibiotic eye drops are prescribed, they can shorten the duration of symptoms, particularly in the first two to five days. Your doctor may prescribe drops or an ointment depending on the severity and your specific situation. For contact lens wearers or more severe cases, prompt treatment is more important.
Allergic Cases
Over-the-counter antihistamine eye drops are the first line of defense. Products containing ketotifen (sold under brand names like Zaditor and Alaway) both block the allergic response and stabilize the cells that release histamine, tackling the problem from two angles. Cold compresses also help reduce puffiness and soothe itching. For chronic or severe allergic conjunctivitis, a doctor may prescribe stronger drops that are more targeted.
How Long You’re Contagious
Viral and bacterial conjunctivitis are both very contagious. They spread through direct contact with eye discharge, contaminated hands, or shared items like towels and pillowcases. You should stay home from work or school if you have systemic signs of illness or can’t avoid close contact with others. You can generally return once any prescribed treatment has been started and a clinician gives approval. Allergic and irritant conjunctivitis pose no risk to the people around you.
To reduce spread, wash your hands frequently, avoid touching or rubbing your eyes, don’t share towels or eye makeup, and replace contact lenses and their cases. If only one eye is affected, be careful not to transfer discharge to the other eye with your fingers.
Pink Eye in Newborns
Newborns can develop conjunctivitis from bacteria picked up during delivery, including chlamydia and gonorrhea. Herpes viruses and other bacteria normally present in the birth canal can also cause infection, sometimes with severe eye damage. This is why most states require hospitals to apply antibiotic ointment (typically erythromycin) to a newborn’s eyes within two to three hours of birth. In the past, silver nitrate drops were used, but antibiotic ointment has largely replaced them.
Symptoms That Need Prompt Attention
Most conjunctivitis is a nuisance, not a danger. But certain symptoms suggest something more serious is going on. Significant eye pain (beyond mild grittiness), severe light sensitivity, blurred vision that doesn’t clear when you blink, or symptoms that worsen after several days rather than improving all warrant a prompt eye exam. Contact lens wearers who develop pink eye should remove their lenses immediately and get evaluated, since the risk of corneal complications is higher.