<Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes little or no problem in most people . These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis . Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling . Food intolerances and food poisoning are separate conditions . </P> <P> Common allergens include pollen and certain food . Metals and other substances may also cause problems . Food, insect stings, and medications are common causes of severe reactions . Their development is due to both genetic and environmental factors . The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine . Diagnosis is typically based on a person's medical history . Further testing of the skin or blood may be useful in certain cases . Positive tests, however, may not mean there is a significant allergy to the substance in question . </P> <P> Early exposure to potential allergens may be protective . Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines . In severe reactions injectable adrenaline (epinephrine) is recommended . Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites . Its use in food allergies is unclear . </P>

A substance that causes an allergic reaction triggers the release of a class of substances known as