Food allergy is an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger signs and symptoms such as digestive problems, hives or swollen airways. Allergies occur when your immune system reacts to a foreign substance. The most common food allergy causing foods are peanuts, milk, eggs, tree nuts, fish, shellfish, soy, and wheat. In other words it is food abnormal responses to harmful foods. A food allergy is also known as food hypersensitivity. The immune system works to protect the body and creates food-specific antibodies. The antibodies are proteins that battle antigens, substances that are foreign or initially outside the body. The introduction of an antigen produces the immune response. Antibodies are created to destroy the antigen or counteract its effectiveness. Food allergies are caused by the immune system reaction to a food item that it believes is harmful. When the food is digested, the immune system responds by creating immunoglobulin E (IgE) antibodies as a defense. The antibodies are proteins found in the bloodstream. Formed to protect the body against harmful substances, the antibodies are created after the persons first exposure to the allergen.