Allergies are diseases of the immune system that cause an overreaction to substances called "allergens." Allergies are grouped by the kind of trigger, time of year or where symptoms appear on the body: indoor and outdoor allergies (also called "hay fever," "seasonal," "perennial" or "nasal" allergies), food and drug allergies, latex allergies, insect allergies, skin allergies and eye allergies. Allergy is caused by any substance, such as pollen, mold or animal dander that can trigger an allergic response. Watery eyes, sneezing, a runny nose, itchy eyes and nose are common symptoms of allergy. People who have allergies can live healthy and active lives.