Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to page options Skip directly to site content


Español: Causas

The most common causes of conjunctivitis (pink eye) are

  • viruses
  • bacteria
  • allergens

It can also be caused by

  • chemicals
  • contact lens wear (especially wearing lenses overnight)
  • foreign bodies in the eye (like a loose eyelash)
  • indoor and outdoor air pollution caused, for example, by chemical vapors, fumes, smoke, or dust
  • fungi

It can be difficult to determine the exact cause of conjunctivitis because some symptoms may be the same no matter the cause.

Viral Conjunctivitis

Girl Sneezing

  • Caused by infection of the eye with a virus
  • Can be caused by a number of different viruses, such as adenoviruses
  • Very contagious
  • Sometimes can result in large outbreaks depending on the virus

Bacterial Conjunctivitis

  • Caused by infection of the eye with certain bacteria
  • Can be caused by Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus species, or, less commonly, Chlamydia trachomatis
  • Very contagious
  • A leading cause of children being absent from daycare or school [1]
  • More common in kids than adults

Allergic Conjunctivitis

  • The result of the body's reaction to allergens, such as pollen from trees, plants, grasses, and weeds; dust mites; molds; dander from pets; medicines, or cosmetics
  • Not contagious
  • Occurs more frequently among people with other allergic conditions, such as hay fever, asthma, and eczema
  • Can occur seasonally, when allergens such as pollen counts are high
  • Can also occur year-round due to indoor allergens, such as dust mites and animal dander
  • May result, in some people, from exposure to certain drugs and cosmetics

Conjunctivitis Caused by Irritants

  • Caused by irritation from a foreign body in the eye or contact with chemicals, fumes, smoke, or dust
  • Not contagious
  • Can occur when contact lenses are worn too long or not cleaned properly


1 Patel PB, Diaz MC, Bennett JE, Attia MW. Clinical features of bacterial conjunctivitis in children. Acad Emerg Med. 2007;14:1-5.

 Top of Page