If you have a true food allergy, your immune system reacts to the allergen protein in the offending food, resulting in symptoms such as itching, hives or the more severe anaphylaxis. Symptoms usually occur very soon after eating the food. In the highly sensitive, even touching or smelling a food can provoke a reaction.
If you have food intolerance, you have an abnormal physical response to a food or food additive. For instance, if you lack the enzymes needed to break down lactose (milk sugar), you have a lactose intolerance and may develop diarrhea.
While food allergies are more common in children, adults can develop allergies to foods at any time.
If a food allergy is suspected, a physician will take a detailed medical history and perform a physical exam. A patient might then keep a food diary, listing foods eaten and any symptoms occurring afterward. Blood and skin tests are sometimes used too.
Allergic reactions to foods claim the lives of 20 to 100 people a year, estimates Steve Taylor, professor of food science and technology at the University of Nebraska-Lincoln.