Conjunctivitis, also called Pink Eye, is an inflammation of the conjunctiva, the mucous membrane that lines the eyelid and eye surface. The lining of the eye is usually clear. If irritation or infection occurs, the lining becomes red and swollen. Pink eye is very common. People of all ages can get conjunctivitis. It can be caused by infection, exposure to chemicals and irritants or allergies, and it usually is not serious and goes away within 7 to 10 days without medical treatment.