An allergy is an immune reaction to a foreign antigen (often protein) - in this case, to a food item.

Do you start itching whenever you eat peanuts? Does seafood cause your stomach to churn? Symptoms like these cause millions of Americans to suspect that they have a food allergy. But true food allergies affect a small percentage of people. Experts estimate that only 2 percent of adults, and from 2 to 8 percent of children, are truly allergic to certain foods.

Food allergy is different from food...