Causes
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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 smoke, dust, fumes, or chemical vapors
- 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
- Infection of the eye caused by 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
- Infection of the eye caused by 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
- Children with conjunctivitis without fever or behavioral changes can usually continue going to school
- 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
Conjunctivitis Caused by Irritants
- Caused by irritation from a foreign body in the eye or contact with smoke, dust, fumes, or chemicals
- Not contagious
- Can occur when contact lenses are worn longer than recommended or not cleaned properly