Allergic Conjunctivitis (ocular allergy*) is the most common allergy affecting the eyes. Many people with allergies experience allergic conjunctivitis when their eyes come in contact with an allergen. The allergen triggers the release of histamine. This typically results in itching, redness, burning or tearing of the conjunctivae (the thin membranes lining the eyelids and the exposed surface of the eyes). Allergic conjunctivitis can be seasonal or perennial. The seasonal version is much more common. It is related to exposure to airborne allergens such as grass, tree and weed pollens or molds. The perennial form persists throughout the year and is usually triggered by dust mites, animal dander or molds. Irritants such as cigarette smoke, strong odors or fumes are not necessarily allergens, but they can make symptoms worse.