• Section 4. Food Allergy Symptoms, Diagnosis, and Testing

    Section Summary

    The following topics are included in this section:

    • Food allergy symptoms
    • Diagnosis and the role of the Dietitian
    • Types of allergy testing


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    Food Allergy Symptoms

    Food allergy reactions can cause a variety of symptoms that range from mild to severe, including anaphylaxis, a serious reaction that is rapid in onset and may cause death. These reactions can be the result of the immune system producing an antibody, Immunoglobulin E (or IgE) to a certain food, or the result of a non-IgE reaction, which is cell-mediated. Some examples of non-IgE reactions include milk or soy intolerances, celiac disease, Food Protein Induced Enterocolitis (FPIES), and eosinophilic disorders.

    The American College of Allergy, Asthma, and Immunology reports that virtually any food can cause an adverse reaction, though eight foods (egg, milk, peanut, tree nuts, fish, shellfish, wheat, and soy) account for approximately 90 percent of all reactions.10

    The National Institute of Allergy and Infectious Diseases recommends that a healthcare professional should consider the diagnosis of food allergy if the person is experiencing anaphylaxis, a severe allergic reaction to food that involves more than one body system (for example, skin and respiratory tract and/or gastrointestinal (GI) tract) or if the person is experiencing a combination of symptoms within minutes to hours after eating food and/or after eating a specific food on more than one occasion.11

    Symptoms can involve the skin, gastrointestinal, cardiovascular, and/or respiratory tracts. Mild symptoms can include an itchy mouth, isolated hives, or mild nausea or discomfort. More severe food allergy symptoms include:

    • Vomiting
    • Stomach cramps
    • Indigestion
    • Diarrhea
    • Hives all over the body 
    • Shortness of breath
    • Wheezing
    • Repetitive cough
    • Tight, hoarse throat; trouble swallowing
    • Swelling of the tongue and/or lips
    • Weak pulse
    • Pale or blue coloring of skin
    • Dizziness or confusion

    The following chart summarizes the symptoms of allergic reactions caused by food.

    Symptoms of a food allergy typically occur within the first few minutes following ingestion of the food allergen, though in some cases, the reaction may be delayed by 4 to 6 hours, or even longer if the reaction is not IgE-mediated (i.e., FPIES).

    Certain symptoms can point to a particular type of reaction –  symptoms such as itchy mouth and throat that could signal Oral Allergy Syndrome (OAS), which occurs in individuals who have hay fever and eat certain raw fruits or vegetables that cross-react with pollens.

    Delayed (two to eight hours) allergic reactions to certain foods such as milk and soy among infants and young children could be related to FPIES, a reaction typically characterized by vomiting and diarrhea. 

    Some mild food related symptoms may be caused by food intolerance rather than an allergic reaction. If you have a reaction to what you believe is a food, consult with your allergist for a diagnosis and to determine a treatment and management plan. 

    Diagnosis and the Role of the Dietitian                          

    The Dietitian has a critical role in both diagnosing a suspected food allergy and supporting and helping patients manage a food allergy reports The International Food Information Council (IFIC) Foundation.

    The first step in the diagnosis of a suspected food allergy is a series of questions to identify suspected foods and determine what further tests should be done to verify food allergy.12

    National Institute of Allergy and Infectious Diseases recommends the following list of questions.

    1. Does anyone in the family have allergies? If so, who has allergies and to what are they allergic?
    2. What are the typical symptoms of the reaction and what is the order in which the symptoms occur?
    3. Did the reaction cause any breathing, skin and/or digestive symptoms?
    4. What was the length of time between consumption of the suspected food and the first sign of reaction?
    5. How much food was eaten to trigger the reaction?
    6. Does a similar reaction occur each time the food is eaten?
    7. Were any prescription medications or over-the-counter drugs taken at the time of the reaction?
    8. Have there been any recent changes in living situation, for example new pets, remodeling, move to a new home, etc.?
    9. How was the reaction treated? How long did it take to resume your normal activities?

    If a food allergy is suspected the patient should be referred to the primary care physician or a board-certified allergist.  The dietician’s role is to support the physician and allergist during the diagnostic procedure by helping the patient to complete a food diary and to assist with the supervised diets and tests.

    Types of Allergy Testing

    Allergy TestSkin tests often are used to diagnose allergies. These tests involve little discomfort and take about 30 minutes to perform. An allergist/immunologist interprets the results of the test in conjunction with the patient's history and uses these results to determine the best course of treatment. Treatment may include medications and allergy shots (immunotherapy).


    There are two types of skin tests:

    1. Prick tests - involve placing small drops of common allergens on the skin (usually on the forearms or back) and then lightly pricking the skin through the drop with a small needle.
    2. Intradermal (i.e., under the skin) tests - involve injecting a small amount of allergen into the outer layer of skin. When a patient is allergic to a substance, redness, itching, and swelling develop at the site of the test within 20 minutes. After the test, a mild cortisone cream may be applied to reduce itching.

    Patch tests can be used to diagnose contact dermatitis. In this test, the allergist/immunologist places a small amount of allergen on the skin (usually on the back), covers the area with a bandage, and checks for a reaction after 48-72 hours. Patients who are allergic to the substance develop a rash, or even blisters, on the skin.

    Certain medications (e.g., antihistamines, antidepressants) and skin conditions (e.g., eczema) can interfere with allergy skin tests. Patients who must continue to take these medications and patients who have a severe skin condition may require a blood test to diagnose allergies. Allergy blood tests involve taking a blood sample, adding an allergen to the sample, and measuring the amount of immunoglobulin E (IgE) antibodies produced in response to the allergen.

     Types of allergy blood tests include the following:

    • Enzyme-linked immunosorbent assay (ELISA)
    • In vitro basophil histamine release assay
    • Radioallergosorbent test (RAST)

    Allergy blood tests, which are less sensitive and more expensive than skin tests, are usually reserved for rare cases when allergy skin tests may not be accurate (e.g., when the patient has sensitive skin that reacts to a saline prick test or has a skin condition, such as hives or eczema, that prevents an adequate field for skin tests).

    In addition to allergy skin tests and allergy blood tests, patients with a suspected food allergy may undergo food allergy tests. Food allergy testing often begins with keeping a food diary, which is a detailed list of all foods, the date and time they were eaten, and any symptoms that occurred.

    When a single food allergy is suspected, the patient may be advised to eliminate the food from the diet and then, if symptoms are relieved, add the food back to the diet to determine if an allergic reaction occurs. This allergy test is not used in patients with a history of severe allergic reaction (anaphylaxis).

    If the results of these food allergy tests are inconclusive, the allergist/immunologist may perform a "blinded" food allergy test and/or a challenge test. These tests usually are performed in a physician's office or in the hospital, and they are closely supervised. They involve feeding the patient either the suspected food, or a neutral food (called a placebo), and then monitoring the patient for an allergic reaction. Neither the patient nor the physician knows whether the suspected food or the placebo is being given to the patient. The results of these allergy tests are very reliable.13

    Section 3. Prevalence of Food AllergiesSection 5. Common Food Allergies