Food allergy is an abnormal response to a food triggered by your body's immune system.
 
In adults, the foods that most often trigger allergic reactions include fish, shellfish, peanuts, and tree nuts, such as walnuts. Problem foods for children can include eggs, milk, peanuts, tree nuts, soy, and wheat.
 
The allergic reaction may be mild. In rare cases it can cause a severe reaction called anaphylaxis. Symptoms of food allergy include
Itching or swelling in your mouth
Vomiting, diarrhea, or abdominal cramps and pain
Hives or eczema
Tightening of the throat and trouble breathing
Drop in blood pressure