Conjunctivitis is inflammation of the mucous membrane that lines the front of the eye and the inside of the eyelids. It can be caused by an infection or an allergy. Either viruses or bacteria can cause infective conjunctivitis, but it is not possible to determine the cause just by looking.

Only one, or both eyes, may be affected and the person will usually complain of a gritty or itchy sensation in the eye(s) for a few days. The eyes will usually be a bit red and have a watery or opaque discharge that can make the eyelids stick together after sleep.

The condition does not usually cause pain in the eyes oraffect vision. Conjunctivitis will usually get better on its own within about a week.