Pink Eye: Causes and How It Spreads

Key points

  • Pink eye caused by viruses or bacteria is very contagious.
  • Allergens and irritants can also cause pink eye, but these are not contagious.
  • Sometimes it is hard to determine the cause because some symptoms are the same no matter the cause.
Man stands outside rubbing his eyes because of pink eye.


Most common causes of pink eye are viruses, bacteria, and allergens.

Less common causes include irritants such as:

  • Chemicals
  • Contact lens wear
  • Foreign bodies in the eye (like a loose eyelash)
  • Indoor and outdoor air pollution caused by smoke, dust, fumes, or chemical vapors
  • Fungi
  • Ameba and parasites


  • Very contagious and sometimes can lead to large outbreaks depending on the virus.
  • Cause: A number of different viruses, such as adenoviruses.
  • Occurs: Viral pink eye can also occur with a common cold or respiratory infection.


  • Very contagious and can spread easily with certain bacteria and in certain settings. More common in kids than adults, especially shortly after birth.
  • Cause: Certain bacteria.
  • Occurs: More frequently from December through April; can occur at the same time as an ear infection.


  • Not contagious from person to person. More common among people with other allergic conditions, such as hay fever, asthma, and eczema.
  • Cause: Body's reaction to allergens, such as pollen from trees, plants, grasses, and weeds; dust mites; molds; dander from pets; medicines; or cosmetics
  • Occurs:
    • Seasonally when allergens such as pollen counts are high.
    • Year-round due to indoor allergens, such as dust mites and animal dander.


  • Not contagious from person to person.
  • Cause: Irritation from a foreign body in the eye or contact with smoke, dust, fumes, or chemicals
  • Occurs: When contact lenses are worn longer than recommended or not cleaned properly

How it spreads

Pink eye caused by viruses and bacteria can easily spread from person to person in different ways.

You can get pink eye from:

  • Close personal contact, such as touching or shaking hands.
  • Contact with droplets from the air after an infected coughs or sneezes.
  • Touching objects and surfaces with germs on them, then touching your eyes before washing your hands.
A child outdoors with itching eyes because of pink eye.
Pink eye can spread if you rub your eyes and don't wash your hands.

Prevent getting or spreading pink eye by practicing good hygiene, including washing your hands often for at least 20 seconds.