Pink eye, also known as conjunctivitis, is a common condition that causes inflammation of the conjunctiva—the thin, clear tissue that lines the inside of the eyelid and covers the white part of the eyeball. When this area becomes inflamed, the blood vessels become more visible, giving the eye a pink or reddish appearance. Pink eye can affect one or both eyes and can be highly contagious, especially in environments like schools and crowded places.