Food allergy is an abnormal response to a food triggered by your body's immune system. Allergic reactions to food can sometimes cause serious illness and death. Tree nuts and peanuts are the leading causes of deadly allergic reactions called anaphylaxis. In adults, the foods that most often trigger allergic reactions include Fish and shellfish, such as shrimp, lobster and crab Peanuts Tree nuts, such as walnuts Eggs Problem foods for children are eggs, milk (especially in infants and young children) and peanuts. Sometimes a reaction to food is not an allergy. It is often a reaction called "food intolerance". Your immune system does not cause the symptoms of food intolerance. However, these symptoms can look and feel like those of a food allergy.