There are three main categories of conjunctivitis: allergic, infectious and chemical:

1. Allergic conjunctivitis

Conjunctivitis may also be caused by environmental allergens such as pollen and is often seasonal. Allergic Conjunctivitis occurs more commonly among people who are already diagnosed with seasonal allergies when they come into contact with a substance that triggers an allergic reaction in their eyes.

Giant papillary conjunctivitis is a type of allergic conjunctivitis caused by the chronic presence of a foreign body in the eye. This condition occurs predominantly with people who wear hard or rigid contact lenses, wear soft contact lenses that are not replaced frequently, have an exposed suture on the surface or the eye, or have a glass eye.

1. Infectious conjunctivitis

• Viral infection - Viral infections are the most common cause of conjunctivitis. This same virus produces the symptoms of a common cold. Symptoms of conjunctivitis can last from one to two weeks and then will disappear on their own.
• Bacterial infection - Bacterial infectionss, such as staphylococcus or streptococcus, cause a type of conjunctivitis that produces considerable amounts of pus. Some bacterial infections, however, are more chronic and may produce little or no discharge except for some mild crusting of the eyelashes in the morning.
• STDs - Sexually transmitted diseases like Chlamydia and Gonorrhea are less common causes of conjunctivitis.

1. Chemical conjunctivitis
   
   Chemical Conjunctivitis can be caused by irritants like air pollution, chlorine in swimming pools, and exposure to noxious chemicals. Allergic checmical reactions to contact lens products, eye drops, or eye ointments can also cause pink eye.

How long is pink eye contagious?
Bacterial conjunctivitis is contagious as soon as symptoms appear and remains contagious as long as there is a discharge from the eye - or until 24 hours after topical antibiotics are started. Viral conjunctivitis is generally contagious before symptoms appear and can remain so as long as the symptoms last. Allergic and irritant conjunctivitis are not contagious.

Pinkeye usually does not affect vision. However, infectious pink eye can easily spread from one person to another. But how do you know if you are exhibiting the signs of pink eye? Do you know the common symptoms of this common eye infection? Learn more about the symptoms of pink eye in the Conjunctivitis Symptoms section that follows.