Causes of Pinkeye (Conjunctivitis)

Viral conjunctivitis often is caused by the same viruses that cause the common cold (called adenoviruses). It also may be caused by herpes simplex virus and the virus that causes measles. Symptoms of viral conjunctivitis can last up to 2 weeks, but they eventually go away without treatment.

Bacterial infections—such as Streptococcus, Staphylococcus, or STDs (e.g., chlamydia, gonorrhea)—can cause a different type of conjunctivitis. Bacterial conjunctivitis usually results in more severe symptoms (e.g., pus in the eye) than viral infection; however, some bacterial infections are chronic and produce only mild crusting of the eyelids in the morning.

Allergic conjunctivitis is not caused by an infection. This form of pinkeye is a symptom of an allergic reaction to allergens, such as pollen or pet dander. Allergic conjunctivitis is not contagious and often is seasonal.

Risk Factors for Pinkeye (Conjunctivitis)

Viral and bacterial conjunctivitis are highly contagious. Family members and people who are in close contact with each other, such as in schools, daycare centers, and summer camps, often spread the infection from person to person.

Children who wear contact lenses, especially extended-wear lenses, may be more prone to developing bacterial conjunctivitis.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 27 Aug 2008

Last Modified: 08 Sep 2015