Is It Food Allergies or Intolerance?

Approximately 8 percent of children and 2 percent of adults suffer from true food allergies. When the culprit food is eaten, most allergic reactions will occur within minutes.

Jar of peanut butter with a "stop" visual sign cut into the top and peanuts scattered all around on a white background
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Skin symptoms (itching, urticaria, angioedema) are the most common and occur during most food reactions. Other symptoms can include:

  • Nasal: sneezing, runny nose, itchy nose and eyes
  • Gastrointestinal: nausea, vomiting, cramping, diarrhea
  • Respiratory: shortness of breath, wheezing, coughing, chest tightness
  • Vascular: low blood pressure, light-headedness, rapid heartbeat​, losing consciousness (syncope)

When severe, this reaction is called anaphylaxis, a condition that can be life-threatening and requires immediate treatment with epinephrine and follow-up emergency medical care.

Allergy or Intolerance?

Most reactions to food are probably not allergic in nature, but rather intolerance. This means that there is no allergic immune response to the food in the person.

Intolerance can be classified as toxic and non-toxic. Toxic reactions would be expected to occur in most people if enough of the food is eaten (examples include alcohol, caffeine, or cases of food poisoning). Non-toxic food intolerance occurs only in certain people. An example is lactose intolerance, which is due to the deficiency of lactase, the enzyme that breaks down the sugar in milk and dairy foods. People with lactose intolerance experience bloating, cramping, and diarrhea within minutes to hours after eating lactose-containing foods, but do not experience other symptoms of food allergies.

Non-Allergic Immunologic Reactions

A less common form of non-allergic reactions to food involves the immune system, but there are no allergic antibodies present. This group includes celiac sprue and food protein-induced enteropathy syndromes, or FPIES. FPIES typically occurs in infants and young children, with gastrointestinal symptoms (vomiting, diarrhea, bloody stools, and weight loss) as the presenting signs. Milk, soy, and cereal grains are the most common triggers for FPIES. Children typically outgrow FPIES by 3 years of age.

Common Childhood Food Allergies

Milk, soy, wheat, eggs, peanut, tree nuts, fish, and shellfish comprise more than 90 percent of food allergies in children. Allergies to milk and eggs are by far the most common and are usually outgrown by the age of 5. Peanut, tree nut, fish, and shellfish allergies are typically more severe and potentially life-threatening, and frequently persist into adulthood. However, any food can occasionally cause a severe or life-threatening reaction. For example, milk and eggs commonly do not cause severe reactions, but, rarely, some individuals develop life-threatening anaphylaxis with small exposures to them.

Cross-Reactivity and Cross-Contamination

Cross-reactivity refers to a person having allergies to similar foods within a food group. For example, all shellfish are closely related; if a person is allergic to one shellfish, there is a strong chance that a person is allergic to other shellfish. The same holds true for some types of tree nuts. For example, there is cross-reactivity between walnuts and pecans, and between cashews and pistachios.

Cross-contamination refers to a food contaminating another, unrelated food. For example, peanuts and tree nuts are not related foods. Peanuts are legumes and are related to the bean family, while tree nuts are true nuts. There is no cross-reactivity between the two, but both can be found, for instance, in a can of mixed nuts, where each cross-contaminate the other. More generally, when a food is processed in a manufacturing plant where an allergen is also processed, that food may be cross-contaminated with the allergen, even though the allergen was not an initial ingredient in the food product.


The diagnosis is made with an appropriate history of a reaction to a specific food, along with a positive test for the allergic antibody against that food. Testing for the allergic antibody can be performed with skin or blood tests.

Blood testing—called a radioallergosorbent, or RAST, test—is often superior to skin prick testing, but there are benefits to both. Nuances of when to choose which test can be discussed with your allergist and are based on factors in your history and symptoms, as well as the resources available to your doctor.

If the diagnosis of food allergy is in question despite testing, an allergist may decide to perform an oral food challenge for the patient. This involves having the person eat increasing amounts of the food, over time and under medical supervision, to see whether an allergic reaction occurs. Since the potential for life-threatening anaphylaxis exists, this procedure should only be performed by a physician experienced in the diagnosis and treatment of allergic diseases. An oral food challenge is one of the best ways to remove a diagnosis of food allergy in a patient.


Treat the reaction: If a severe reaction to the food is present, the person should seek immediate emergency medical care. Most patients with food allergies should carry a self-injectable form of epinephrine, or adrenaline (such as an Epi-pen®, with them at all times. This medication can be prescribed by a physician, and you should know how to use this device before an allergic reaction occurs.

Oral immunotherapy: This form of treatment may help decrease severe allergic reactions by exposing you to very small amounts of an allergen, then slowly increasing such exposure over time. A new oral immunotherapy product for peanut allergy, Palforzia, was approved by the FDA in January 2020 and is the only such product currently on the market. It is not a cure for peanut allergy, but may decrease the risk of severe allergic reactions to peanuts. If you choose to use this treatment, you should still carry epinephrine at all times.  

Avoid the food: This is the main way to prevent future reactions to the culprit foods, although it can be difficult in cases of common foods such as milk, egg, soy, wheat, and peanut. Learn how to avoid the most common food allergens. Organizations such as the Food Allergy Research & Education offer help and support to patients and parents of children with food allergies. Allergy physicians can also offer additional information and advice on avoidance.

Read food labels: Since accidental exposure to the allergic food is common, reading labels on foods and asking questions about ingredients at restaurants is important and recommended.

Be prepared: Patients with food allergies should always be prepared to recognize and treat their reaction should one occur. Remember, since exposures to the allergic foods are frequently accidental, being prepared to treat the reaction with epinephrine is paramount. Emergency medical care should always be sought if an allergic reaction to food occurs, whether or not epinephrine is used.

Communicate with others: Communication with family members, friends, and school staff about the patient’s medical condition and knowledge of how to administer epinephrine is also important. It is also recommended that the patient wear a medical ID bracelet (such as a Medic-Alert® bracelet) detailing their food allergies and use of injectable epinephrine in the case the patient is unable to communicate during a reaction.

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  • The American Academy of Allergy, Asthma and Immunology, and Food Allergy Practice Parameters. Ann Allergy Asthma Immunol. 2006; 96:S1-68.
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