How can you tell the difference between viral pink eye, bacterial pink eye, and allergies?

Some differences: Generally viral pink eye typically produces redness, watery eyes and doesn't need treatment except for herpes. Bacterial pink eye causes redness & purulent discharge (puss), often "matting the lids/lashes together" in the AM or after a long nap -- needs antibiotic drops. Allergies almost always involve both eyes with redness, some watering, & can be quite itchy. Consult doc if you have it.