DEAR MAYO CLINIC: I have struggled with stomach issues for many years. Is it possible my upset stomach can be an allergy or sensitivity to certain foods? I want to feel better, and I am curious about testing that may be available to identify food sensitivities and food allergies.

ANSWER: Gastrointestinal issues are challenging, and it can be difficult to identify what may be causing you distress. It is important to recognize that food allergies and food sensitivities are not interchangeable terms.

A food allergy is the body’s immune response where an immunoglobulin E antibody, also known as an allergy antibody, binds to an allergy cell. The allergy cell releases chemicals, namely histamine, that causes a reaction — typically within a few minutes. Though rare, there is the possibility of a delayed reaction of up to two hours after time of contact with the allergen. The most typical allergic reactions include itching, hives, rash, or an anaphylactic reaction, where breathing becomes impaired.

Approximately 32 million people in the U.S. have food allergies. The most common allergens are peanuts, tree nuts, fish and crustacean shellfish, wheat, soy, sesame, milk, and eggs.

When someone has difficulty processing or digesting a food properly, that is known as a food intolerance or food sensitivity. Intolerance occurs in the intestines, and it is related to how people break down components or enzymes of what they eat. Lactose intolerance, for instance, is a common food sensitivity. People who are sensitive to lactose do not have enough enzymes to break down the lactose in food and beverages, which will cause symptoms. Use a food diary to track what food you had prior to having symptoms. If you note anything in your diet that is different, try taking it out.

There is no immune response in a food intolerance or sensitivity, and it does not harm a person. But it can be uncomfortable. Symptoms can include extreme bloating, fullness, abdominal pain or cramping, brain fog, headaches, and altered stool patterns of loose stools or constipation.

In most situations, a food allergy will cause a more immediate reaction; whereas, food sensitivities may develop over time — anywhere from 30 minutes up to four or five hours later, which is the average time it takes for food to move from the stomach.

It can be challenging for some people to determine if they have a food allergy or a sensitivity, and a health care professional should make the diagnosis.

Food allergy testing

The gold standard of allergen testing is a skin test, where a small amount of an allergen is placed on the skin — typically on the back or forearm. Next the skin is gently scratched to introduce the allergen into the skin. Within 10‒15 minutes, histamine is released, and a red bump will appear if there is possibly an allergy. The size of the redness and bump determine if an allergy is present and the severity.

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