Pink eye (conjunctivitis) is an inflammation or infection of the transparent membrane (conjunctiva) that lines your eyelid and covers the white part of your eyeball. When small blood vessels in the conjunctiva become inflamed, they're more visible. This is what causes the whites of your eyes to appear reddish or pink.
Pink eye is commonly caused by a bacterial or viral infection, an allergic reaction, or — in babies — an incompletely opened tear duct.
Though pink eye can be irritating, it rarely affects your vision. Treatments can help ease the discomfort of pink eye. Because pink eye can be contagious, early diagnosis and treatment can help limit its spread.