Chemosis is a symptom characterized by swelling of the conjunctiva, the transparent membrane that lines the eyelids and covers the whites of the eyes. It is usually caused by an allergic reaction or infection and can vary in severity from mild to severe. Symptoms usually start with itching, redness, and burning of the eyes, followed by swelling of the conjunctiva and a feeling of tightness in the eyes. In more severe cases, the eyes may appear to bulge out of the eye sockets.