Conjunctivitis is the inflammation of the conjunctiva (the membrane that lines the eyelids and covers the exposed surface of the eyeball).

Conjunctivitis can be caused by allergies, bacteria, viruses, chemicals, or underlying health conditions.

The eyes are susceptible to infection because they are not sterile. They rely on lysozyme (an enzyme found in the tears) to destroy bacteria. Bacteria line the surface of the eyelids (all the way down into the shaft of the eyelashes), which makes the...