The outer most layer of the eye is called the conjunctiva. When this becomes inflamed and irritated it is called conjunctivitis. Causes can include allergies, getting material such as soap in the eye, viral and bacterial infections. One or both eyes can be affected. The most frequent cause is a viral infection which is commonly called "pink eye" because the conjunctival blood vessels dilate and give the conjunctiva a pink hue. Treatment depends on the cause.