Although most eye inflammations result in a pink discoloration of the eye (because of dilated blood vessels in the conjunctiva), doctors usually use the term "pink eye" for conjunctivitis caused by infection with a bacterium or virus.

One of the most severe forms of pink eye is the result of infection with several particular strains of adenovirus. This infection, called epidemic keratoconjunctivitis (see table ), is extremely contagious and often results in large outbreaks within a community or school. The infection is spread through contact with infected secretions. Such contact may take place person-to-person or through contaminated objects, possibly including improperly disinfected doctors’ instruments.

Many symptoms of epidemic keratoconjunctivitis, such as redness and thin, watery discharge and, less commonly, irritation and sensitivity to light, are similar to those of other types of viral conjunctivitis. However, some people with epidemic keratoconjunctivitis feel like grit or sand is in their eye and can have pain when the eye is exposed to bright light. The conjunctiva can swell and bulge around the cornea. Many people develop a swollen lymph node in front of the ear on the affected side. These symptoms typically last from 1 to 3 weeks. Some people have blurred vision, which may last for weeks or months before resolving.

Epidemic keratoconjunctivitis resolves completely without specific treatment. Doctors sometimes give corticosteroid drops to people with very blurred vision or severe sensitivity to light. Good hygiene, particularly the use of hand sanitizers, is needed to minimize the spread of the infection. Separate towels, washcloths, and bedding help minimize the spread to other members of the household. People generally stay home from work or school for several days or, in severe cases, even weeks.