Inflammation of the mucous membrane that covers the surface of the eye and the underside of the eyelids. The condition can be caused by bacteria, viruses or irritation of the eye by an allergy or harmful substances. The commonest cause is a viral infection, usually during influenza or a cold, often first on one side only, then spreading to both. The eye becomes red, and weeps. The membrane swells, and small bubbles can form inside the eyelid. The eye smarts, the patient becomes hypersensitive to light, and the whole eye can swell. Conjunctivitis occurs about two weeks after the eye is infected with the virus. A viral infection heals spontaneously, and medication is unnecessary. Viral conjunctivitis can sometimes develop into the bacterial form. Symptoms are the same, but more severe. Discharge from the eyes contains pus, and the patient’s eyelashes are stuck together on waking in the morning. Bacterial inflammation starts about two days after the eye is infected with bacteria. A possible complication is ulceration of the cornea. Treatment is by antibiotics in the form of eye drops or ointment. Conjunctivitis can also be caused by an allergy, for example in the case of hay fever, and should then be treated by anti-allergic medication. Sometimes the cause is an irritant substance such as eyeliner, smoke or chemicals, and treatment is then by avoiding contact with such materials.