Allergic Conjunctivitis Grass pollen   Allergic conjunctivitis occurs when the airborne allergens settle on the lining of your eye and cause inflammation of the inside of the eyelids. The symptoms include:   Itchy and watery eyes   Reddening of the eyes   Swelling of the eyelids   Seasonal allergic conjunctivitis is caused by an allergic reaction to tree, grass, or weed pollen. This occurs mainly in children and young adults and it is usually associated with rhinitis. The timing of onset depends on the type of sensitization and when pollination occurs.   For perennial allergic conjunctivitis, it occurs all year round, with symptoms similar to the seasonal disease but usually less severe. Household allergens are the major cause of perennial allergic conjunctivitis. About 80% of the sufferers are allergic to house-dust allergens, and around 33% also suffers from rhinitis.