Allergies, or allergic diseases, are conditions caused by hypersensitivity of the immune system to food or substances in the environment. The body can react to allergens in a number of ways and symptoms can include sneezing, itchy eyes, coughing and rashes. A severe allergic reaction can result in anaphylaxis shock. Medicines such as antihistamines can be used to stop a reaction from occurring. Common allergies include: pollen, dust, nuts, animal dander and medicine.