Pink eye is caused by inflammation (redness, swelling) or infection of the conjunctiva(the membrane lining the eyelids). “Pink eye” is mostly referred to as viral conjunctivitis (viral infection of the conjunctiva) which is more frequent among children. Therefore the inflammation of the conjunctive (conjunctivitis) may be caused by exposure to bacteria and many other irritants. Over-the-counter tears help your conjunctiva eliminate away a large portion of the growing bacteria, prescribed tears also contain antibiotics that kill bacteria. There are many etiologies of conjunctival inflammation, viruses are the most common one; also allergies (allergic conjunctivitis, which is very itchy), bacterial, autoimmune, chlamydial infection, fungal, parasitic but rare, contact allergy (by contact lenses)