Allergies, also recognized as allergic diseases, are a number of circumstances caused by hypersensitivity of the immune system to something in the environment that usually causes little difficulty. These diseases comprise hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may comprise red eyes, an itchy rash, runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate circumstances.