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What Are Food Allergies?

Food allergies are overreactions by the immune system to specific foods. These allergies can cause varied symptoms, some of which are severe and potentially life-threatening.

Studies estimate that at least 8% of children and 5% of adults experience food allergies. Testing can identify food allergies so that they can be more easily avoided and treated.

How is food allergy different from food sensitivity and intolerance?

A food allergy is distinct from a food sensitivity or intolerance. The key difference is that an allergy involves the immune system while most intolerances or sensitivities are related to the gastrointestinal system.

Examples of non-allergic reactions to food include lactose intolerance (an inability to properly digest a sugar found in milk products), sensitivity to caffeine, and intolerance to gluten. While these can cause bothersome symptoms, they don’t provoke an excessive immune response and are not allergic reactions.

Other important differences usually found between food allergies and intolerances and sensitivities include:

  • For food allergies, the quantity consumed often doesn’t matter, and even contact of the food with the skin may provoke a reaction. For intolerances and sensitivities, increased consumption usually worsens symptoms.
  • Symptoms tend to be the same each time for intolerances and sensitivities. In contrast, reactions after allergen exposure can vary in the type of symptoms and their severity, including the possibility of life-threatening reactions.

Food allergy testing is focused on identifying things that trigger the immune system, and, as a result, is distinct from food sensitivity testing.

The Role of Food Allergy Tests

Food allergy tests help diagnose a specific allergy. They are used after someone has already shown signs of an allergic reaction. It is rare to do food allergy testing if someone has not shown symptoms of allergies.

After an allergy diagnosis, testing can be used to monitor whether a person is still allergic. Many food allergies go away over time, especially in children, and this kind of follow-up testing can help determine whether they can safely consume a food that they previously had an allergic reaction to.

When should testing be done?

Experts recommend food allergy testing only after symptoms of an allergy have occurred.

There is no single test to look for all food allergies, and tests can show signs of an allergy when no real allergic reaction occurs. This is known as a false positive result. Because a test that looks for all possible allergens can return many false positives, doctors normally order food allergy tests that look only for specific allergens based on your history of symptoms.

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Types of Food Allergy Tests

Several different types of tests can be used to determine if you have a food allergy. Some tests involve direct exposure to a suspected allergen, and, for your safety, these tests must be done in a medical setting with a health professional.

  • The skin prick test involves putting a drop of a possible allergen on your skin and then poking that area with a very small needle to let the substance get just beneath the top layer of skin. Even though you don’t eat the food, an allergic reaction is still detected in the skin. This test must be performed under careful medical supervision in case a severe reaction occurs.
  • An allergy blood test measures levels of proteins called immunoglobulin-E (IgE) that can be elevated when you have an allergy to a specific food.
  • An oral food challenge includes eating progressively larger amounts of a food at specified intervals over a period of a few hours. During the test, you are closely monitored by a doctor to see if there is an allergic reaction and to immediately treat a severe reaction if it occurs.
  • Food elimination is not a strict testing method, but it may be employed to prepare for other tests and to see if avoiding a food reduces allergy symptoms. Food elimination generally requires carefully controlling your diet for a period of time to ensure that you have no exposure to one or more potential allergens.

While other types of tests may be marketed as food allergy tests, experts and professional organizations discourage their use because they are not proven to accurately determine when a person has a true allergy.

Getting Tested for Food Allergies

Allergy tests are usually ordered by a doctor. Before prescribing a test, the doctor asks about your symptoms and when they occured to try to identify the most likely allergen to test for. You may also be referred to an allergist, a specialist in diagnosing and treating allergies.

Many allergy tests must be performed under medical observation because of the possibility of a severe reaction. Tests with direct exposure are virtually always done in a hospital, clinic, or doctor’s office.

Blood tests for food allergies do not involve exposure and do not require the same precautions. A blood sample may be taken in a doctor’s office or laboratory and then sent for analysis.

At-home testing

At-home test kits are available for food allergy blood testing. These tests involve pricking your finger and putting one or more drops of blood on a test strip. You then mail the test strip to a laboratory that analyzes your blood immunoglobulin for signs of a potential allergy.

A positive test result alone cannot diagnose a food allergy. Instead, a doctor must evaluate your symptoms and health history along with any test results. When you discuss your symptoms with your doctor prior to testing, the doctor can look for the most likely allergens. However, this is not possible with at-home tests that look for a predetermined list of allergens.

Because allergy blood testing can return false positive results, your doctor will likely want to do follow-up testing if your at-home test indicates that you may have an allergy.

Sources and Resources

These resources offer background information about food allergies and their symptoms, causes, and treatment:

Sources

A.D.A.M. Medical Encyclopedia. Allergies. Published February 2, 2020. Accessed March 21, 2021. https://medlineplus.gov/ency/article/000812.htm

Burks W. Diagnostic evaluation of food allergy. In: Sicherer SH, ed. UpToDate. Updated April 23, 2019. Accessed March 21, 2021. https://www.uptodate.com/contents/diagnostic-evaluation-of-food-allergy

Burks W. Patient education: Food allergy symptoms and diagnosis (Beyond the Basics). In: Sicherer SH, ed. UpToDate. Updated January 22, 2021. Accessed March 21, 2021. https://www.uptodate.com/contents/food-allergy-symptoms-and-diagnosis-beyond-the-basics

Carr S, Chan E, Lavine E, Moote W. CSACI Position statement on the testing of food-specific IgG. Allergy Asthma Clin Immunol. 2012;8(1):12. Published 2012 Jul 26. doi:10.1186/1710-1492-8-12

Commins SH. Food intolerance and food allergy in adults: An overview. In: Sicherer SH, ed. UpToDate. Updated May 28, 2020. Accessed March 21, 2021. https://www.uptodate.com/contents/food-intolerance-and-food-allergy-in-adults-an-overview

Consumer Reports and the American Academy of Allergy, Asthma & Immunology. Allergy Tests: When you need them and when you don’t. Published July 1, 2012. Accessed March 23, 2021. https://www.choosingwisely.org/patient-resources/allergy-tests/

Keet C, Wood RA. Food allergy in children: Prevalence, natural history, and monitoring for resolution. In: Sicherer SH, ed. UpToDate. Updated January 8, 2019. Accessed March 26, 2021. https://www.uptodate.com/contents/food-allergy-in-children-prevalence-natural-history-and-monitoring-for-resolution

Kelso JM. Unproven and disproven tests for food allergy. In: Sicherer SH, ed. UpToDate. Updated June 4, 2020. Accessed March 21, 2021. https://www.uptodate.com/contents/unproven-and-disproven-tests-for-food-allergy

Kowal K, DuBuske L. Overview of in vitro allergy tests. In: Bochner BS, ed. UpToDate. Updated February 5, 2021. Accessed March 21, 2021. https://www.uptodate.com/contents/overview-of-in-vitro-allergy-tests

Kowal K, DuBuske L. Overview of skin testing for allergic disease. In: Bochner BS, Wood RA, eds. UpToDate. Updated April 3, 2020. Accessed March 21, 2021. https://www.uptodate.com/contents/overview-of-skin-testing-for-allergic-disease

Lavine E. Blood testing for sensitivity, allergy or intolerance to food. CMAJ. 2012;184(6):666-668. doi:10.1503/cmaj.110026

MedlinePlus: National Library of Medicine. Allergy. Updated May 16, 2018. Accessed March 21, 2021. https://medlineplus.gov/allergy.html

MedlinePlus: National Library of Medicine. Food allergy testing. Updated July 31, 2020. Accessed March 22, 2021. https://medlineplus.gov/lab-tests/food-allergy-testing/

National Academies of Sciences, Engineering, and Medicine. Finding a Path to Safety in Food Allergy: Assessment of the Global Burden, Causes, Prevention, Management, and Public Policy. The National Academies Press; 2017. Accessed March 22, 2021. https://www.nap.edu/catalog/23658/finding-a-path-to-safety-in-food-allergy-assessment-of

Pawankar R, Holgate ST, Canonica W, Lockey RF, Blaiss MS, eds. White Book on Allergy 2013 Update. World Allergy Organization; 2013. Accessed March 21, 2021. https://www.worldallergy.org/UserFiles/file/WhiteBook2-2013-v8.pdf

Sicherer SH. Oral food challenges for diagnosis and management of food allergies. In: Wood RA, ed. UpToDate. Updated June 17, 2019. Accessed March 22, 2021. https://www.uptodate.com/contents/oral-food-challenges-for-diagnosis-and-management-of-food-allergies

Turnbull JL, Adams HN, Gorard DA. Review article: the diagnosis and management of food allergy and food intolerances. Aliment Pharmacol Ther. 2015;41(1):3-25. doi:10.1111/apt.12984

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