allergies center

How Are Food Allergies Done?

Reviewed on 1/6/2023
A boy receives an allergy test
There are many foods that people might be allergic to. Tests used to diagnose food allergies include a skin test, blood tests, and a food challenge.  
An allergy occurs when the body’s immune system sees a substance as a harmful “invader” and overreacts to it. Substances that trigger an immune response (an allergic reaction) are called allergens.  

Allergy testing can help determine if you are allergic to certain foods. Allergists are doctors who specialize in diagnosing and treating allergies and they can determine which test will best detect the food allergens that cause allergy symptoms. 

Some of the most common food allergens include: 

  • Peanuts
  • Tree nuts
  • Eggs
  • Wheat
  • Cow’s milk 
  • Shellfish 
  • Fish
  • Soy
  • Mustard
  • Sesame and other seeds
  • Gluten

Skin tests are the most accurate allergy tests, though blood tests may also be used, to help determine a patient’s reaction to common food allergens. 

Skin tests for allergies are done in an allergist’s office. Prior to the test, tell your doctor about any medications you take, both prescription and over-the-counter (OTC), because some medicines may interfere with skin testing.

Tests used to diagnose food allergies include: 

  • Skin test 
    • A small scratch is made on the skin and a small amount of liquid extract of the food is applied
    • If there is a reaction, such as a raised spot (wheal or hive), skin redness, or itching, it usually means there is an allergy
  • Blood tests
    • Antibody test: The blood is drawn and sent to a lab where it is mixed with the allergen and checked for IgE antibodies, a type of protein the body produces when it has an allergic reaction
    • Component testing: Looks for IgE to several different proteins found in the foods, to give the doctor additional information about the allergy and the best way to manage it
  • Food challenge
    • Involves gradually eating a serving of suspected food and seeing whether it causes symptoms
    • Usually done only when other tests are not clear or to check if an allergy has gone away
    • For safety reasons, this test must be done ONLY in a doctor's office or hospital
      • Do not attempt to do a food allergy challenge test at home, as a severe life-threatening allergic reaction (anaphylaxis) could occur
      • A doctor’s office or hospital has medications to treat severe allergic reactions

What Are Symptoms of Food Allergies?

Symptoms of a food allergy usually occur within minutes to hours after eating the food and may include: 

When to call 911

Some of the above symptoms may be severe and could be signs of a serious and potentially life-threatening allergic reaction (anaphylaxis). Sudden, severe, widespread reactions require emergency care. Call 911 if you suspect someone is having a severe allergic reaction. 

How Are Food Allergies Treated?

The best treatment for a food allergy is to avoid the food, and also any meals that may contain that food as an ingredient. 

  • Read food labels carefully
    • Some foods may not contain the known food allergen but are produced in factories that make other items that contain the known food allergen
    • Equipment may be used for both types of foods and cross-contamination may occur
  • Some countries (including the U.S.) have laws that require companies to clearly list whether a food contains certain food allergens (such as nuts, dairy, or egg) 
    • Check food labels for phrases such as:
      • “May contain ‘the known food allergen’” 
      • "Produced on shared equipment with ‘the known food allergen’” 
  • When dining out, inform servers of the food allergy
  • Make sure children know what foods they can and cannot eat
  • If a food allergen is accidentally ingested, antihistamines may help treat minor reactions 
  • Have an emergency plan
    • Antihistamines may be used for mild reactions, but are not a substitute for epinephrine if a severe allergic reaction (anaphylaxis) occurs
    • People with a diagnosed severe food allergy should have a shot of epinephrine with them at all times if recommended by their doctor
    • Epinephrine injection comes in an easy-to-carry dispenser
    • Parents should notify a child’s teachers, the school nurse, coaches, parents of the child’s friends, and anyone else who may care for the child to know what a reaction looks like and how to respond
      • These people should also know how to reach the parents and the child’s doctor in case of emergency
    • After epinephrine is administered, the child should be taken to the hospital or another medical facility to be monitored for at least 4 hours to make sure the reaction is under control and does not come back

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Reviewed on 1/6/2023
References
Image source: iStock Images

https://acaai.org/allergies/testing-diagnosis/#allergy-testing

https://www.aaaai.org/Conditions-Treatments/Allergies/Food-Allergy

https://kidshealth.org/en/kids/nut-allergy.html

https://www.uptodate.com/contents/peanut-allergy-the-basics?search=peanut%20allergy&source=search_result&selectedTitle=1~69&usage_type=default&display_rank=1