Acute conjunctivitis is common and highly infectious. Usually it is caused by a virus (e.g. adenovirus) but it may be bacterial (e.g. Staphylococcus). Acute conjunctivitis may occur in outbreaks in schools. Measles, tickbite fever and tuberculosis may also cause acute conjunctivitis.
Conjunctivitis due to allergy may be recurrent or chronic, and is usually associated with other allergies.