Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that normally causes little problem. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.Common allergens include pollen and food.