Pink Eye Causes

People develop pink eye for a number of different reasons. Causes of the condition may include a viral infection, a bacterial infection, or an allergic reaction. In most cases, the causes of pink eye are related to a virus (most commonly adenovirus) or the allergens that cause both seasonal and year-round allergy symptoms.

What Causes Pink Eye?

Pink eye is medically known as conjunctivitis. Conjunctivitis is inflammation of the conjunctiva, which is the thin piece of tissue that covers the whites of the eyes and the inner eyelids.
 
There are several reasons why the conjunctiva can become inflamed. The two most common are because of an infection with a virus (known as viral conjunctivitis) or an allergic reaction (allergic conjunctivitis). An infection with bacteria can also cause pink eye (bacterial conjunctivitis).
 

Viral Causes

Most cases of pink eye are caused by a virus -- in particular, adenovirus. Adenovirus is the same virus that often causes the common cold. This is why viral conjunctivitis often occurs following a recent upper respiratory tract infection such as the common cold.
 
Symptoms of viral conjunctivitis may include a watery, mucous discharge; red and swollen eyelids; and, of course, a red or pink eye. This type of pink eye typically starts in one eye and, after a few days, moves to the other eye.
 
Other viruses can cause conjunctivitis, including:
 
  • Herpes simplex virus
  • Varicella zoster virus (the virus that causes chickenpox and shingles)
  • Molluscum contagiosum.
     

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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD
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