Pink eye is a layman's term for the medical condition conjunctivitis. Conjunctivitis is inflammation of the conjunctiva, which is the thin piece of tissue that covers the whites of the eyes and the inner eyelids. When the conjunctiva becomes inflamed, it looks pink or red from a distance.
Pink eye is a common condition. It is most common in children, but adults may also get pink eye. This condition does not usually cause any long-term vision or eye problems.
There are several reasons why the conjunctiva can become inflamed. The two most common are because of an infection with a virus (known as viral conjunctivitis) or an allergic reaction (allergic conjunctivitis).
An infection with bacteria (bacterial conjunctivitis) or something that irritates the eye, such as an eyelash, can also cause the conjunctiva to become inflamed.
Besides conjunctivitis, there are a number of other conditions that can cause a red or pink eye. Some of these conditions can be potentially serious.
(Click Pink Eye Causes to learn more about the different types of conjunctivitis and what else can cause a red or pink eye.)