An allergy is a specific immunologic reaction to a substance that is usually harmless. These sensitizing substances, or allergens, may be inhaled, injected, swallowed or touched. Common Allergens People can be allergic to one or more allergens. Pollen from trees, grasses and weeds House dust mites, found in mattresses, pillows and carpets Animal allergens Mold spores Cockroaches Certain foods and medicines Venom from insect stings Chemicals used in industry Allergen Effects on the Body People who are susceptible to developing allergies produce IgE antibodies when an allergen is absorbed into the body.
Antibodies are substances produced in response to bacteria, viruses and allergens.
These antibodies counteract or destroy bacteria and viruses. In allergic individuals, however, when these allergy-related antibodies react with the allergens, special cells known as mast cells are activated. This reaction causes irritation and swelling in sensitive areas of the body, such as the nose, eyes, lungs, skin and digestive system. Initially, a person may not be sensitive to an allergen, but may develop sensitivity after repeated exposure, sometimes after years of exposure. Hay fever can be a seasonal or year-round health problem.