How do i know if i have pink eye or is it just blood shot?

Allergic/Viral/Bacte: Pink eye is lay mans term used for redness in the eye which can be caused by different conditions allergic conjunctivitis little redness, swelling and itching viral infection especially adenovirus, herpes zoster, can be with severe pain, intolerance to light and vision problem baterial infection which will present with redness, discharge and pain subconjunctival hemorrhage redness only, no pain/itching.