Conjunctivitis, also called pinkeye, is an inflammation of the conjunctiva, the transparent membrane that lines the eyelids and covers the whites of the eyes. Conjunctivitis can be triggered by allergies, by contact with irritating chemicals, or by infections with either a virus or bacteria.
Viral conjunctivitis often is caused by one of the adenoviruses, a family of viruses that usually causes colds (upper respiratory illnesses). In temperate climates, adenoviruses are most active during spring, early summer and mid-winter. They infect fluids in the eyes, mouth and nose, and can spread from person to person on hands and in the droplets of coughs and sneezes. In most cases, adenoviruses cause only a mild case of conjunctivitis. However, they are capable of causing a more serious infection, called kerato-conjunctivitis, which can cloud the cornea and interfere with vision. Besides adenoviruses, other viruses that cause conjunctivitis include enteroviruses, the measles virus (rubeola) and the herpes simplex virus.
Bacterial conjunctivitis can be caused by several different types of bacteria, including Haemophilus influenzae, pneumococci, staphylococci (staph) and streptococci (strep). Most bacterial infections spread through contact with hands that have been contaminated with the bacteria. Children born to mothers with gonorrhea or chlamydia also can develop conjunctivitis if their eyes are infected by contaminated secretions in the birth canal during vaginal delivery