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Español: Causas

The most common causes of conjunctivitis (pink eye) are

  • viruses
  • bacteria
  • allergens

Other causes include

  • chemicals
  • contact lens wear
  • 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
  • ameba and parasites

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 influenzae, Moraxella catarrhalis, or, less commonly, Chlamydia trachomatis and Neisseria gonorrhoeae
  • Can be spread easily, especially with certain bacteria and in certain settings
  • A leading cause of children being absent from daycare or school [1]
  • More common in kids than adults
  • Observed more frequently December through April

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 longer than recommended 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.

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