Pink eye, the common name for conjunctivitis, is an inflammation or infection of the conjunctiva, the outer, normally clear covering of the sclera, the white part of the eye. The eye appears pink in conjunctivitis because the blood vessels are dilated. Pink eye is often accompanied by a discharge, but vision is usually normal, and discomfort is mild.

Either a bacterial or a viral infection may cause conjunctivitis. Viruses, which are more common and last several weeks, may cause an upper respiratory infection (or cold) at the same time. Unlike viruses, bacterial conjunctivitis is treated with a variety of antibiotic eye drops or ointments, which usually cure the infection in a day or two.

Conjunctivitis can be very contagious. People who have it should not share towels or pillowcases and should wash their hands frequently. They may need to stay home from school or work and should stay out of swimming pools.

Not everyone with conjunctivitis has an infection. Allergies can cause conjunctivitis too. Typically, people with allergic conjunctivitis have itchy eyes, especially in spring and fall. Eyedrops to control itching are used to treat allergic conjunctivitis. It is important not to use medications that contain steroids (they usually end in “-one” or “-dex”) unless prescribed by an ophthalmologist.

Finally, not everyone with pink eye has conjunctivitis. Sometimes more serious diseases, such as infections, damage to the cornea, very severe glaucoma, or inflammation on the inside of the eye cause the conjunctiva to become inflamed and pink. Vision is usually normal if the pink eye is really conjunctivitis. If vision is affected, or if the problem does not get better in a few days, see an ophthalmologist.