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Diagnosing Food Allergies

Medically reviewed by Chhavi Gandhi, MD, Susan Kerrigan, MD and Marianne Madsen on January 14, 2023

When was the last time you received a packet of peanuts on an airplane? These tiny bags of crunchy snacks once kept little flyers happy and engaged for the two minutes it took to chew and swallow.  Yet nowadays peanuts are a rare sight in any public space. 


With the rise of allergy awareness, institutions have become more conscientious about keeping customers with allergies safe. Schools and camps enforce strict policies monitoring what foods kids can and can’t bring for lunch. In today’s age, allergies are some of the most well-known dietary conditions. But how much do we really know about it? Do we know how to recognize the signs of an allergic reaction or how doctors diagnose a patient with allergies? What is an allergy exactly? Here’s a walk through the diagnostic process for food allergies to help you understand what to expect.


What are allergies?


Allergic reactions take on a range of symptoms, from mild to life-threatening. Yet all allergies begin in the immune system. Under normal circumstances, your immune system is your friend. It helps fight diseases caused by harmful bacteria or viruses. Yet sometimes the immune system can get confused. It might treat something innocent such as a dust spot–or peanut–like a dangerous invader. The immune system sounds the alarm and begins releasing chemicals that cause allergic reactions.  These reactions are very uncomfortable–or even dangerous–for the body. Children often discover food allergies unexpectedly after eating a food that suddenly elicits a reaction. If you have good reason to suspect that your child may have an allergy, you can take her to an allergist. The allergist will run a few tests to understand the nature of the allergy.


How do I know it’s a food allergy?


While some allergies can be hard to detect, food allergies are easier to identify because, in most cases, one starts reacting immediately after eating. During an allergic reaction, someone might experience swelling in the face, mouth, or throat area; hives; itching; dizziness; and trouble breathing. In some cases the symptoms won’t appear right away but can manifest hours later.


Anaphylaxis, a severe allergic reaction involving one or more body areas, can be life threatening. If you notice that someone around you is having trouble breathing or speaking or is experiencing swelling in the mouth or throat, call an ambulance immediately. If they have an  epinephrine injector , find out where it is and help them administer it. Symptoms that can be indicative of an anaphylactic reaction are rash or hives on the body, swelling, flushed skin, abdominal pain, nausea, vomiting, racing heart rate, shortness of breath, coughing, wheezing, dizziness and loss of consciousness. 


Not all reactions to food are caused by allergies. You may experience stomach problems or other symptoms that are caused by a food intolerance.  A food intolerance, unlike an allergy, is not a response from the immune system. Furthermore, sometimes food intolerances can be managed by medication, and you may be able to eat small quantities of the trigger food. There are many reasons why a patient may suffer from a food intolerance. The best thing is to speak with a doctor to learn why your body is reacting this way. If your doctor suspects that you may have an allergy, she will refer you to an allergist who will determine whether or not it is an allergy.


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Anaphylaxis - Symptoms

Anaphylaxis - Symptoms

How are allergies diagnosed?


There are at least 3 different tests an allergist might use to help diagnose a food allergy:


  • Skin test: The allergist will place a small drop of food in liquid form onto the skin. Then she will use a needle to lightly prick the allergen into the skin. If the skin turns red and blotchy after 15 minutes, there may be a food allergy. However the allergist will not make a diagnosis unless the patient has also experienced symptoms. 
  • Blood test: If the patient can’t undergo the skin test for medical reasons, the allergist will take a sample of her blood. The sample will be sent to a lab where it will be introduced to different allergens. The lab will measure the amount of antibodies in the blood. If the blood has more antibodies than normal, it may think that it is under attack by the allergen. This can be indicative that the patient has an allergy.
  • Challenge test: The patient will inhale or swallow a small amount of the allergen under the guidance of an allergist. This is the most definitive allergy test, since both blood and skin tests can have false positives. However, only patients who do not have a history of severe allergic reactions can perform the challenge test.


Treating allergies


Avoidance is the best way to treat any food allergy. There are some people who can tolerate a small amount of food allergens, but in general it’s best to stay away from foods that trigger an allergic reaction. However, if someone does have exposure to a food they are allergic to, there are a few medications that can alleviate the symptoms. For someone prone to anaphylaxis, an injection of epinephrine (adrenaline) can stop symptoms of a reaction. If you start to feel an attack coming on, immediately use the epinephrine auto-injector even if you’re not sure whether it is a serious reaction. Epinephrine is a safe-to-use medication. If you inject it under a “false alarm,” the consequences will be minimal. In addition to epinephrine, antihistamines can also be used to treat mild reactions. Some name-brand antihistamines are Benadryl and Zyrtec. Epinephrine is always the first line treatment for anaphylactic reactions and antihistamines should only be used for mild symptoms such as a few hives or mild rash after eating an allergic food. Speak with your Allergist for further recommendations on the use of medications during an allergic reaction.


Living with Food Allergies


Living with a food allergy can be more challenging than living with other types of allergies. Often patients newly diagnosed with a food allergy will need to make lifestyle changes such as being more mindful about what they eat. This may require reading ingredient labels more closely and asking more questions about menu items in restaurants. They might also need to educate their friends and acquaintances about their dietary needs. People with allergies also need to keep their medication on hand at all times. 


With all the inconveniences of having an allergy, the most difficult part of living with allergies might be the feeling of “standing out from the crowd.” It’s not always easy having to tell friends or coworkers, “No, sorry. I can’t eat that.” Depending on the severity of the allergy, a dinner invitation, a cocktail party, or a night at a restaurant can require tremendous mental maneuvering. “Do I tell the hostess that I can’t eat shellfish, or should I just avoid it at the table?” “Is there anything on the menu I can eat or should I bring my own food?” However, the world is gradually changing. People are learning more about each other’s individual differences and uniqueness. The popularity of diets such as veganism and keto have brought into question whether we should assume that everyone can eat from the same plate. Whether it’s a medical restriction, lifestyle choice, religious practice, or personal preference, there are many reasons why someone may decide to eat differently. 


Written by Chani Bonner

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