Acute conjunctivitis. Close-up of the bloodshot eye of a patient with acute conjunctivitis. Conjunctivitis is inflammation of the conjunctiva, the membrane that covers the surface of the eye and lines the eyelids. Causes include allergic reactions, such as hay fever, and infection by bacteria or viruses. Symptoms may include redness, irritation, itching, and a discharge, which may be clear and watery or yellow, indicating infection. One of the most common medical complaints, conjunctivitis accounts for over 2% of visits to the doctor. Treatment depends on the cause and severity.