DEAR MAYO CLINIC: I'm a grandmother to three wonderful grandchildren. My oldest grandchild is lactose intolerant. Recently, my youngest grandchild was diagnosed with a peanut allergy. What is the difference between food intolerance and allergy?

ANSWER: Life at the dinner table is different for thousands of people in the U.S. living with a food allergy. Recent studies show that approximately 5% of children under the age of 5 and 3% of adults have food allergies.

Food allergies and intolerances often are confused for one another. The symptoms can be similar.

If you have a food allergy, your body overreacts to a specific food as if it were a threat. This can occur when you ingest even the smallest amount of the food. For some people, the allergy may be triggered by smelling or coming into contact with the food.

When you come into contact with the food, your immune system releases an antibody called immunoglobulin E to neutralize the food allergen.

The immunoglobulin antibodies tell your immune system to release a chemical called histamine, which causes many allergic symptoms, such as itching, swelling, hives and difficulty breathing.

The top eight most common food allergens are egg, milk, peanuts, shellfish, tree nuts, soy, fish and wheat.

Unlike an allergic reaction, the symptoms of food intolerance are typically gastrointestinal. An intolerance means your body does not have the correct mechanisms to digest certain foods properly.

A common food intolerance is lactose — the main sugar in milk products. If you have lactose intolerance, your body has difficulty digesting lactose, causing symptoms of bloating, abdominal pain and sometimes diarrhea.

Other intolerances that are sometimes confused with food allergy include:

• Irritable bowel syndrome — a condition causing frequent diarrhea, constipation, bloating and other gastrointestinal symptoms when excess short-chain carbohydrates are consumed
• Celiac disease — a condition where the body sustains damage at a microscopic level from ingesting gluten, which is found in wheat, barley or rye products
• Food poisoning caused by bacteria that contaminate food

An allergist is the best qualified professional to diagnose a food allergy. Your allergist will begin by taking a detailed medical history to find out whether your symptoms are an allergic reaction, an intolerance or another health problem.

Other food allergy tests include:

• Skin test
  A skin test may determine which foods, if any, trigger your allergic symptoms. In skin testing, a small extract of the food is placed on your forearm or back by a tiny pinprick just below the skin. You'll develop a small bump if you're allergic to the substance.
• Blood test
  Your allergist also may take a blood sample to measure the levels of food-specific immunoglobulin E. Positive blood tests do not necessarily mean that you have a food allergy, but they can help put together the pieces of the puzzle.
• Food diary
  You may be asked to keep a food diary of what you eat and whether you have a reaction.
• Elimination diet
  A limited elimination diet is removing the suspected food allergen from your diet under the direction of your health care professional for a few weeks. You then add the food item back into your diet to see if the symptoms return.
• Oral food challenge
  During this test, conducted in your allergist's office, you are given small, but increasing amounts of the suspect food. Your health care professional watches you to see whether a reaction occurs. A reaction only to suspected foods confirms the diagnosis of a food allergy. If you don't react, you may be able to include that food in your diet again.

Unfortunately, those with food allergies cannot be cured. You can only prevent the symptoms by avoiding the foods that cause a reaction. If you come into contact with a food that causes a minor allergic reaction, you often can use an antihistamine to reduce the symptoms. For severe reactions, you may need an emergency epinephrine injection or a trip to the emergency department. You should always wear a medical alert bracelet or necklace. Seek medical care if you suspect you are having an allergic reaction. —Kjersten Nett, R.D.N., Clinical Nutrition, Mayo Clinic Health System, Albert Lea and Austin, Minnesota

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Related Article 

• Mayo Clinic Q and A: Testing for food allergies and sensitivities published 4/13/22

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