Conjunctivitis also known as Pink eye is an inflammation of the thin, clear covering of the white of the eye and the inside of the eyelids (conjunctiva). Although the conjunctiva is transparent, it contains blood vessels that overlay the sclera of the eye. Anything that triggers inflammation will cause these conjunctival blood vessels to dilate. This is what causes red, bloodshot eyes.

Conjunctivitis can have several causes, but many eye doctors use the term "pink eye" to refer only to viral conjunctivitis, a highly contagious infection caused by a variety of viruses.

What Causes Pink Eye?

The primary types of conjunctivitis, based on cause, are:

Viral conjunctivitis Caused by a virus, like the common cold. This type of pink eye is very contagious, but usually will clear up on its own within several days without medical treatment.

Bacterial conjunctivitis Caused by bacteria, this type of conjunctivitis can cause serious damage to the eye if left untreated.

Allergic conjunctivitis Caused by eye irritants such as pollen or dust or in some cases animals.