Conjunctivitis is the term used to describe swelling (inflammation) of the conjunctiva — the thin, filmy membrane that covers the inside of your eyelids and the white part of your eye (known as the sclera). Often this condition is called "pink eye."
The conjunctiva, which contains tiny blood vessels, produces mucus to keep the surface of your eye moist and protected. When the conjunctiva becomes irritated or swollen, the blood vessels become larger and more prominent, making your eye appear red. Signs of pink eye may occur in one or both eyes.
There are three types of conjunctivitis:
This is a highly contagious form of pink eye caused by bacterial infections. This type of conjunctivitis usually causes a red eye with a lot of pus.
The most common cause of pink eye is the same virus that causes the common cold, and is also very contagious.
This form of conjunctivitis is caused by the body's reaction to an allergen or irritant. It is not contagious.
Source: American Academy of Ophthalmology, www.geteyesmart.com