The eye, like the respiratory tract, can be a site of acute allergic reactions. Ocular allergy also called Allergic conjunctivitis occurs when something allergic to irritate the conjunctiva. This is the sensitive membrane covering the eye and the inside of the eyelid. As all allergies, allergic conjunctivitis starts when the immune system recognises an otherwise innocuous substance as an allergen. This causes your immune system to overreact and produce antibodies called Immunoglobulin E (IgE). These antibodies drive to cells that release chemicals which cause an allergic reaction. In this case, allergic reactions include eyes that water, itch, hurt or become red or swollen.