Eye allergy (Conjunctivitis)
The surface of the eye is directly exposed to the environment and hence, a variety of airborne particles can land directly on the surface of the eye tissues. Some particles can cause irritation which often associated with an inflammatory reaction. In eye allergy the main tissue that is affected is the mucous membrane (called conjunctiva) of the eye. The conjunctiva is a thin clear membrane that covers the white portion of eyeball and the inside of the eyelids. It gets inflamed and very itchy in the allergic process. Rubbing the eye increases the itchiness. The majority of eye allergy is caused by environmental allergens such as house dust mites, pollens, pet dander, cockroach, bird droppings and other air borne allergen particles. Food allergens such as shrimp, crab and similar foods, may be important in some individuals. Occasionally severe eye allergy may cause serious damage to the eyes threatening eyesight.

Contact ocular allergy is another form of eye problem that is non-IgE mediated and initiated often by preservatives in eye drop medication or sometimes the medication itself may be the cause of the problem. In this case the eye remains distressed as long as the eye medication is continually used. Sometimes the application of cosmetics that contain the offending preservatives may cause inflammation of the eyelids and trigger reaction in the conjunctiva. In recent years the use of contact lens has resulted in the development of another type of eye allergy triggered by the lens.