The conjunctiva is exposed to bacteria and other irritants. Tears help protect the conjunctiva by diluting bacteria and washing it away.
Tears also contain enzymes and antibodies which inhibit bacterial growth.
Conjunctivitis is the most common eye disease in the western hemisphere and varies in severity from mild inflammation with tearing to a severe inflammation that causes tissue injury and tissue death. There are many causes of conjunctivitis. Viral and bacterial forms of conjunctivitis are highly contagious, and can spread among children very rapidly, sometimes causing local epidemics. Newborns can be infected by bacteria in the birth canal. This condition is called ophthalmia neonatorum and must be treated immediately to preserve sight.