Acute conjunctivitis is inflammation of the thin, transparent membrane that covers the white of your eye and lines the inside of your eyelids. It’s one of the most common eye complaints, affecting roughly 13 out of every 1,000 people in the U.S. each year and accounting for about 30 percent of all eye-related emergency department visits. Most people know it as pink eye, and it typically resolves on its own within a few days to two weeks.
What Happens Inside Your Eye
The conjunctiva is a thin tissue rich with tiny blood vessels. When it becomes inflamed, those blood vessels dilate and become more visible, giving the eye its characteristic pink or red appearance. The tissue itself swells, and the eyelids often puff up as well. Depending on the cause, your eye may produce anything from a thin, watery discharge to thick, yellow-green pus. This inflammation is your immune system responding to an infection, allergen, or irritant.
Viral Conjunctivitis
Viruses are the most common cause of acute conjunctivitis in adults, and adenoviruses are the usual culprit. There are over 40 different strains. The hallmark is a watery, mucus-like discharge rather than thick pus. Your eyes will feel gritty or burning, as if something is stuck in them, and you’ll likely notice crusting on your eyelids in the morning. The lids themselves can become red and swollen.
One telltale sign that helps distinguish viral from other types: a small, tender lymph node just in front of your ear on the affected side. If your doctor feels for this, they’re checking for viral conjunctivitis specifically. Occasionally, tiny pinpoint hemorrhages appear on the white of the eye, which looks alarming but resolves on its own.
Some adenovirus strains cause a condition called pharyngoconjunctival fever, where the eye symptoms come alongside a sore throat, headache, and fever. When the infection spreads to involve the cornea (the clear dome over your iris), it’s called epidemic keratoconjunctivitis, a more severe form that can temporarily blur your vision.
Viral conjunctivitis is highly contagious. You remain infectious as long as your eyes are tearing and producing discharge, which typically lasts one to two weeks. There’s no antiviral treatment for the common strains. Recovery relies on your immune system.
Bacterial Conjunctivitis
Bacterial conjunctivitis produces a noticeably thicker, more purulent discharge. Your eyelids may stick together after sleeping, and the discharge is often yellow or greenish. Both the surface of the eye and the inner lining of the eyelids become intensely red and swollen.
The bacteria responsible vary by age. In children, the most frequent causes are certain strains of respiratory bacteria that spread through hand-to-eye contact. In adults, the same organisms appear alongside staph bacteria. A particularly aggressive form, called hyperacute conjunctivitis, produces copious pus and can threaten your vision quickly, requiring urgent treatment.
Most cases of ordinary bacterial conjunctivitis are self-limited, meaning they clear up without antibiotics. A practical approach many doctors use is “delayed prescribing,” where you receive a prescription but are advised to wait three days before filling it. If your symptoms improve on their own, you skip the antibiotics entirely. Studies show this strategy provides the same symptom control as taking antibiotics immediately while cutting antibiotic use in half.
Allergic Conjunctivitis
Allergic conjunctivitis looks and feels different from the infectious types. Itching is the dominant symptom, often intense. Your eyes water, burn, and appear red, but the discharge is clear and watery rather than thick or crusty. Both eyes are almost always affected at the same time.
The underlying mechanism is an allergic reaction. When your eyes encounter an airborne allergen like pollen, dust, or mold, immune cells in the conjunctiva release a flood of histamine and other inflammatory chemicals. This is the same process behind hay fever, and the two conditions frequently occur together. Seasonal patterns are common: tree pollen in spring, grass pollen in summer, weed pollen in fall. Unlike viral or bacterial conjunctivitis, the allergic form is not contagious.
Conjunctivitis in Newborns
Newborn conjunctivitis, called ophthalmia neonatorum, deserves separate attention because it can be more serious. The most common bacterial cause is chlamydia, picked up during delivery. Other bacteria and, less commonly, herpes simplex virus can also be responsible. Symptoms include red, swollen eyelids with watery or mucopurulent discharge, sometimes forming a membrane over the inner eyelid.
To prevent this, hospitals routinely screen pregnant women for chlamydia and gonorrhea and apply antibiotic drops or ointment to a newborn’s eyes shortly after birth. Ironically, these prophylactic drops themselves can cause a mild chemical conjunctivitis that usually clears within a day or two.
How to Tell the Types Apart
The type of discharge is the most useful clue. Thick, yellow-green pus strongly suggests bacteria. Watery discharge with a gritty sensation and a swollen lymph node near the ear points toward a virus. Intense itching with clear, watery eyes and a known allergy history points toward an allergic cause.
That said, the types overlap enough that even doctors sometimes can’t distinguish them on appearance alone. What matters more is recognizing the symptoms that signal something worse than simple conjunctivitis. Severe eye pain, sensitivity to light, blurred vision that doesn’t clear when you blink, a misshapen pupil, or discharge so heavy it reaccumulates within minutes after wiping are all signs that warrant prompt evaluation. These can indicate corneal infection, inflammation deeper inside the eye, or the aggressive bacterial forms that need immediate treatment.
What Helps While You Recover
Cool compresses are the simplest form of relief. Soak a clean, lint-free cloth in cool water, wring it out, and place it gently over your closed eyelids. Some people prefer warm compresses, which can help loosen crusted discharge. The key rule: if only one eye is affected, use a separate cloth for each eye to avoid spreading the infection.
Artificial tears can soothe the gritty, dry feeling. For allergic conjunctivitis, over-the-counter antihistamine eye drops reduce itching. Avoiding your known allergen triggers helps prevent recurrences.
To limit spread of infectious conjunctivitis, wash your hands frequently, avoid touching your eyes, don’t share towels or pillowcases, and replace any eye makeup you used while symptomatic. Keep children home from school or daycare as long as their eyes are visibly tearing and producing discharge. Contact lens wearers should switch to glasses until the infection fully resolves and discard any lenses worn during the illness.