Oral Food Challenges That Can Determine Allergy

Various nuts
Food challenges are used to determine if a person is actually allergic to a certain food.. Toma Evsukova/Stocksy United

Food allergies are a common problem, affecting 8 percent of children and at least 2 percent of adults. The diagnosis of food allergy isn’t always clear, and despite the use of proven diagnostic methods such as skin testing and blood testing, it can be difficult to determine if a person actually has a food allergy.

In fact, a “positive test” doesn’t diagnose a food allergy—simply showing that a person has IgE antibody against a food doesn’t mean that he or she is allergic to that food.

Being allergic to a food means that when a person eats a certain food, the person experiences one or more symptoms that are consistent with food allergy. It is possible and actually common in people with other allergic diseases to make allergic antibodies against various foods and yet be able to eat those foods without apparent reaction. In this circumstance, a person is NOT allergic to the food; this situation is called “asymptomatic sensitization.”

Even when it appears that a person experienced an allergic reaction to food, it may be difficult to determine which food, or foods, actually caused the allergic reaction. This is especially true because most people don’t eat a single food at a time; rather, foods are eaten together in meals, and when eating large meals or eating in restaurant settings, people may eat dozens of foods for a single meal. With prepared foods, it can be especially difficult to determine which food actually caused the allergic reaction.

In many cases, children may outgrow certain types of food allergies. Food allergies such as milk, egg, soy, and wheat are commonly outgrown during childhood; while allergies to peanuts, tree nuts, fish, and shellfish are less likely to be outgrown during one’s lifetime. Allergy skin testing and blood testing for food allergies can be predictive of a person outgrowing a food allergy.

However, since no test is completely accurate, a food challenge may be required to completely know if a person has outgrown a food allergy.

A food challenge can be a helpful tool for all of the above-mentioned situations. Food challenges involve feeding a person a particular food, under medical supervision, while monitoring for symptoms of an allergic reaction. Food challenges can be performed to (1) prove that a person is allergic (or not allergic) to a certain food when the diagnosis is in question AND/OR (2) prove that a person has outgrown a food allergy that was diagnosed at an earlier time. Allergists are uniquely qualified to perform food challenges, which may be performed in a medical office, and in some circumstances, in a hospital setting.

Types of Food Challenges

There are three different types of food challenges, including open challenges, single-blind challenges, and double-blind challenges. An open food challenge involves a patient eating a food that isn’t hidden inside another food in any way.

A patient undergoing an open food challenge knows exactly what they’re eating, and therefore the patient may have a component of bias towards experiencing some type of allergic reaction. Open food challenges are the most common type of food challenge, especially in a community allergist’s office. These types of food challenges are relatively easy to perform and usually take a few hours to complete.

Another type of food challenge is a single-blind food challenge. This means that the patient eating the foods doesn’t necessarily know what they are eating since the suspect food might be mixed inside another food, or even placed inside of gelatin capsules to swallow. The suspect food may or may not be given to the patient on a particular day, and the challenge may last multiple days. This can reduce a patient’s bias towards having an allergic reaction, since the patient may or may not be given the suspect food to eat. The healthcare staff (such as a nurse) administering the food challenge does know if the patient is given the suspect food or not, and therefore the healthcare professional may have some level of bias that is communicated to the patient.

The last type of food challenge is a double-blind, placebo-controlled food challenge, which is similar to a single-blind food challenge, but neither the patient nor the healthcare staff administering the challenge is aware if the patient is eating the suspect food at a particular moment. The suspect food is hidden inside another food or a gelatin capsule. This type of food challenge completely removes any bias of the patient or healthcare staff towards experiencing an allergic reaction. A double-blind placebo-controlled food challenge is typically used in research settings and is too difficult, expensive, and time-consuming to perform in most clinical settings outside of major universities.

Risks vs. Benefits of Performing a Food Challenge

Once your allergist has determined the need for a food challenge, there are a number of items you need to be aware of before proceeding with the food challenge. These questions need to be discussed between doctor and patient prior to the food challenge being performed. First, you must know the reason for the food challenge. Is the diagnosis of food allergy in doubt, or is there reason to believe that the food allergy has been outgrown? Would there be benefit in reintroducing the food back into the person’s diet? Does the person even want to eat the suspect food? What are the chances that the person will “pass” the food challenge? What are the risks of performing the food challenge? What are the benefits?

How to Prepare for a Food Challenge

In order to safely proceed with a food challenge, the patient’s other medical conditions should be as stable as possible. This means that the patient’s nasal allergies (allergic rhinitis), asthma, and atopic dermatitis should be as controlled as possible. A food challenge would be difficult to interpret if the patient is sneezing, coughing, and has itchy skin rashes even before the food challenge has begun. The patient should otherwise not be ill for at least a couple of days prior to the food challenge and be free from fever, vomiting, diarrhea, or new skin rashes.

Non-allergic medical conditions, such as high blood pressure and diabetes, would also need to be controlled prior to performing a food challenge. Given the small but real possibility of an allergic reaction occurring that requires the administration of epinephrine, it is important that the patient’s blood pressure is not out of control prior to the food challenge, as blood pressure could go even higher if epinephrine is administered.

Medications such as antihistamines may need to be stopped for a few days prior to a food challenge. Antihistamines could mask a mild reaction from occurring, but may not prevent a severe reaction. Some allergists also stop certain types of asthma medicines for a day prior to a food challenge, depending on the type of reaction that is anticipated as a result of eating the suspect food.

It is expected that the patient will bring the suspect food into the allergy clinic to eat. The food should be prepared as simple as possible, without added ingredients. It is usually acceptable to spice the food with salt and pepper to the patient’s liking. A full serving of the food to be eaten should be brought to the allergy clinic.

On the morning of the food challenge, the patient should only take those medicines that were approved by the allergist. The patient should either fast or eat only a light meal prior to coming into the allergy clinic. There should be no strenuous exercise on the entire day of the food challenge.

What To Expect During a Food Challenge

The patient should expect to arrive early to the allergy clinic. Vital signs will be taken, and often the allergist or other healthcare professional will perform a brief physical examination prior to the start of the food challenge. Some allergists may place an intravenous (IV) catheter in the patient's arm in case intravenous fluid or other medicines are needed to treat a severe allergist reaction, but this is not typical. Spirometry or other method of lung function testing, to establish a baseline value, may be performed if the patient has asthma. Once it has been determined that the patient is stable, the food challenge will begin.

The patient will first be given a very small amount of the suspect food to eat (or drink), typically starting with milligram amounts. Then, every 15-30 minutes, the patient will eat increasing amounts of the food, all while being monitored by the healthcare staff for signs of an allergic reaction. This process continues until either the patient has tolerated a full serving of the suspect food, or an allergic reaction occurs. If a full serving of the food is tolerated, which is typically multiple grams of food, then the patient will be monitored for another one to two hours to ensure no reaction occurs. The patient will be asked to not eat any more of the suspect food until the following day, in order to monitor for delayed reactions. If no delayed reactions occur, then the patient can (and should) eat that food regularly.

If an allergic reaction occurs during the food challenge, it is likely that the patient will require treatment. Mild symptoms such as itching, hives, or mild upset stomach may be treated with oral antihistamines, such as Benadryl. More severe symptoms, such as swelling of the tongue or throat, asthma symptoms, or low blood pressure should be treated with injected epinephrine.

If any of these symptoms occur, the patient is deemed allergic to the suspect food and the food challenge is stopped. The patient will then be monitored for a period of time, typically a few hours, until he or she is stable and can be sent home. A dose of oral or injected steroids may also be given in order to prevent the allergic reaction from re-appearing many hours later. All patients with a known food allergy should always have an Epi-Pen available to treat an allergic reaction should one occur.


Nowak-Wegrzyn A, Assa’ad AH, Bahna SL, et al. Work Group Report: Oral Food Challenge Testing. J Allergy Clin Immunol. 2009;123:S365-83.

Continue Reading