An allergy is an abnormal reaction by the immune system to the presence of a substance. A substance that produces such a reaction is called an allergen. Allergens can include pollen, dust mites, mold, pet dander, among many other substances. When the body reacts to an allergen, it produces antibodies that attach to certain cells within the body. Those cells are found in the gastrointestinal tracts, the respiratory system, the nose, and the skin. These antibodies work to flush the allergen from the body. The symptoms of an allergy are similar to those of a cold.
