Medical Editor: Barbara K. Hecht, Ph.D.
Sometimes people become sick from eating a particular food, because they cannot properly process or digest the food, or because they have a true allergic (immune) reaction to the food. Food allergies and food intolerance are sometimes confused with each other, but they are quite different in terms of their origin, symptoms and treatment.
True allergic reactions to food involve the body's immune system. When the body identifies a food as harmful, it produces antibodies directed against that food. The next time the food is consumed, the body mounts an immune response with the release of histamine and other chemicals that trigger allergic symptoms. A common example of a food allergy is to peanuts.
With a food allergy, symptoms may occur almost immediately or up to hours after consuming the particular food. These symptoms may affect the respiratory system, gastrointestinal tract, cardiovascular system, or the skin.
Food allergy symptoms can include:
- skin rash or hives,
- swelling of the tongue and throat,
- breathing problems including asthma,
- vomiting or diarrhea, and
- abdominal pain and cramping.
There are no medications that can cure food allergies. Diligent avoidance of the offending food is the only sure way to prevent a reaction. People with food allergies must thoroughly examine food labels and ask questions about the ingredients of dishes. For example, the label on a breakfast cereal may read: "May contain soy, peanuts and/or other tree nuts."
Severe life-threatening allergic reactions can be treated with the prescription drug epinephrine. This drug is available as a pen-style injector.
Food intolerance is different from food allergy in that it does not involve an immunologic reaction. A common type of food intolerance is lactose intolerance. Persons with lactose intolerance lack an enzyme (called lactase) needed to digest the milk sugar (called lactose). They can develop gas, bloating, and abdominal pain when they consume milk products.
Some types of food intolerance can be treated. For example, lactase tablets are available without a prescription to aid those with severe symptoms of lactose intolerance and lactose-free dairy products are available at most supermarkets.
If an individual thinks they may have either food allergy or food intolerance, keep a diary of the foods eaten and any symptoms experienced. A food diary can help the doctor establish the correct diagnosis. A doctor can also order simple skin tests or blood tests to determine if an individual is allergic to specific foods. The strategy of dealing with a food allergy is different than dealing with food intolerance.