Healthcare provider explaining oral allergy syndrome to patient

Oral Allergy Syndrome Explained

Medically reviewed on May 17, 2023 by Jillian Foglesong Stabile, MD, FAAFP. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Table of contents

Oral allergy syndrome (OAS), also called pollen-food syndrome, is a type of food allergy that affects only the mouth, throat, tongue, and lips. Most often, those affected by OAS also experience asthma or hay fever, as a result of cross-reactivity. [1]

Fortunately, OAS reactions are rarely severe and typically manageable, as long as you know what types of foods and plant materials trigger the immune response. [2]

What Is Oral Allergy Syndrome?

Oral allergy syndrome is the most common food allergy in adults. It occurs in individuals who are also allergic to certain types of pollen and other substances, such as birch, ragweed, grass pollen, mugwort, alder, and latex. [2]

In fact, it’s believed that between 47–70% of people with pollen allergies also experience OAS. [2]

So, why does this occur? Proteins in certain foods are similar to the proteins found in some allergenic plant materials. [1] This is called molecular mimicry. Accordingly, the immune system wrongly recognizes these food proteins as pollen allergens, which can trigger an immune response, thus initiating an allergic reaction. [1]

This progression is what’s referred to as cross-reactivity. [3]

More specifically, the immune system produces antibodies called immunoglobulin E (IgE) in response to exposure to pollen allergens. IgE then binds to immune cells in the blood, skin, and organs, triggering them to release histamine, which plays a key role in the body’s inflammatory response. [4]

These antibodies can cross-react with proteins found in raw vegetables, fruits, and nuts, leading to a similar allergic reaction. [1]

That said, there are many potential cross-reactive foods that are similar to certain allergens and may trigger OAS symptoms: [1]

  • Birch – The components in birch are similar to the proteins found in apples, pears, peaches, apricots, cherries, plums, nectarines, prunes, kiwi, carrots, celery, potatoes, peppers, fennel, parsley, coriander, parsnips, hazelnuts, almonds, and walnuts.
  • Ragweed – Bananas, melons, zucchini, cucumber, dandelions, and chamomile tea may trigger an allergic reaction in those with a ragweed allergy.
  • Grass pollen – Proteins in peaches, celery, melons, tomatoes, and oranges are similar to those found in grass pollen.
  • Mugwort – Those with mugwort allergies are advised to avoid celery, apple, kiwi, peanut, fennel, carrots, parsley, coriander, sunflower, and peppers.
  • Alder – Celery, pears, apples, almonds, cherries, hazelnuts, peaches, and parsley may trigger an allergic reaction in those sensitive to alder.
  • Latex – Bananas, avocado, kiwi, chestnut, and papaya protein can mimic the components found in latex, a milky white liquid found in some flowering plants.

Unlike non-IgE-mediated food allergies, which are not triggered by the production of IgE, OAS may lead to anaphylaxis—a severe and potentially life-threatening allergic reaction that can make it difficult to breathe. [5] Fortunately, less than 2% of people with OAS experience anaphylaxis, and food allergy symptoms are typically mild. [2]

Symptoms of Oral Allergy Syndrome

An OAS allergic reaction can occur seconds or minutes after consuming a potential cross-reactive food. In other words, it develops quickly. [2]

Once the immune system recognizes the cross-reactive protein, it’ll trigger a localized immunoinflammatory response in the mouth, lips, tongue, and throat. Individuals with OAS symptoms may experience: [2]

  • Itchy mouth
  • Scratchy throat
  • Tingling
  • Swelling
  • Bumps

Less common symptoms include: [2]

  • Nausea
  • Hives
  • Rash
  • Difficulty breathing
  • Anaphylaxis
  • Itchy, swelling, or red skin where you touched the foods

So, how long does a food allergy reaction last? Typically, symptoms will resolve within a few hours. That said, symptoms of OAS can vary in severity and presentation between individuals, and may even vary for the same individual, depending on the level of allergen exposure. [2]

Diagnosis of Oral Allergy Syndrome

An OAS diagnosis is typically based on clinical history, in addition to a physical examination and allergy testing. In patients with a history of airborne pollen allergies, itching and tingling of the mouth after eating fresh, raw fruits, vegetables, or nuts often points to OAS. [6]

During a physical exam, a healthcare provider will examine the patient’s mouth and throat for signs of swelling or redness. The exam is typically coupled with an allergy test to identify certain allergens, in the form of:

  • Skin prick tests – The skin is lightly pricked with a suspected allergen. The patient is then observed by a healthcare provider to identify signs of an allergic reaction. Results are often immediate.
  • Blood tests – Slightly more invasive, a healthcare provider will extract blood from the patient and examine the levels of IgE antibodies, after exposing the patient to certain food-based proteins. Blood tests are also available as at-home lab tests that you can conduct within your own home. Whether performed at home or in a medical office, results will typically take up to a few days.

A healthcare provider may also administer a food challenge test, in which you’ll be given increasing amounts of certain foods and observed for signs of an allergic reaction. [2]

Management and Treatment of Oral Allergy Syndrome

Unfortunately, there is no designated treatment for OAS. Rather, effective management of OAS involves a combination of strategies that aim to prevent or minimize symptoms and reduce the risk of complications. These can involve: [2]

  • Avoiding potential trigger foods – After undergoing diagnostic allergen tests, most individuals will understand what types of food may trigger an OAS reaction. As such, the most effective way to manage OAS symptoms is to avoid allergens completely to evade potential cross-reactivity.2 If you have seasonal allergies, it’s generally recommended to avoid these trigger foods during these times, as your reaction may be more severe than usual. [2]
  • Immunotherapy – Some healthcare providers may administer allergy shots or sublingual immunotherapy to those with severe OAS reactions or multiple pollen allergies. Over time, individuals are exposed to small amounts of the allergen to help desensitize the immune system to certain pollens and food proteins. [7]
  • Antihistamine medication – Over-the-counter antihistamines can block some of the effects of histamine in the body to reduce the severity of an allergic reaction and reduce inflammation in the mouth, tongue, lips, and throat. [8] Antihistamine medications include Benadryl, Allegra, and Claritin.
  • Epinephrine – Some individuals may carry around an injectable epinephrine pen if they’re prone to severe allergic reactions or anaphylaxis. Epinephrine, also known as adrenaline, helps to relax the muscles and open the airways. [2]

How to Prevent Oral Allergy Syndrome

In addition to avoiding allergens and trigger foods, taking medications, and administering immunotherapy, individuals with OAS may find it helpful to cook raw vegetables, fruits, and nuts before consumption.

Heat can change the structure of certain food proteins, allowing them to bypass the immune system without triggering a cross-reactive allergic reaction. [2]

Who Does Oral Allergy Syndrome Affect?

Generally, it’s unlikely that children under the age of three will experience cross-reactivity, or OAS. Typically, it takes a few years to develop a pollen or food allergy. [2] Also, it’s not unusual for adults to develop pollen or food allergies later in life—particularly if they’ve moved to a new geographical location with vegetation they haven’t yet been exposed to. [9]

So, how exactly do pollen allergies develop?

Allergy development involves two phases: [9]

  • Sensitization – When your body first encounters an allergen, like ragweed, the body will begin making IgE antibodies to defend itself against the new, and potentially harmful, substance. During this phase, however, you’re unlikely to experience an allergic reaction.
  • Reaction – The second time your body encounters an allergen, it’ll take action. The IgE antibodies bind to the allergen and other immune cells to produce histamine and other chemicals that trigger inflammation and other allergy symptoms throughout the body. Within minutes, your mouth, tongue, lips, and throat may begin to tingle or itch.

See related: Are Food Allergies Genetic?

Oral Allergy Syndrome vs. Other Food Allergies

Oral allergy syndrome is often confused with other types of food allergies. However, food allergies and OAS will typically display different allergy symptoms. While signs of OAS are limited to the mouth, tongue, lips, and throat, food allergies can instigate a full-body allergic reaction.

Common signs of a food allergy include: [10]

  • Dizziness
  • Lightheadedness
  • Itchy skin
  • Raised skin
  • Rash
  • Swelling
  • Coughing
  • Wheezing
  • Trouble breathing
  • Sneezing
  • Abdominal pain
  • Diarrhea

Additionally, some food allergies are not triggered by IgE at all. Non-IgE-mediated food allergies are triggered by T cells in the immune system and allergic symptoms are typically isolated to the gastrointestinal tract. [12] Although, in some cases, individuals may experience chronically itchy or blistered skin (in the case of Celiac disease).11 Those with non-IgE mediated food allergies may experience: [11]

  • Nausea
  • Vomiting
  • Diarrhea
  • Dehydration
  • Weight loss
  • Lethargy
  • Abdominal pain
  • Gassiness
  • Lack of appetite
  • Constipation
  • Bloating
  • Shock

These types of food allergies can also develop into several food hypersensitivity syndromes, such as: [11]

  • Food protein-induced enterocolitis syndrome (FPIES)
  • Allergic proctocolitis (AP)
  • Food protein-induced enteropathy (FPE)
  • Celiac disease (specific to gluten allergy)

The Difference Between Food Allergies and Food Intolerance

Food intolerance arises when the digestive system has trouble breaking down certain foods.

Unlike an allergic reaction, the immune system is not triggered if you experience a food intolerance and the symptoms are rarely life-threatening. That said, the symptoms of food intolerance can be similar to a food allergy: Individuals may experience diarrhea, bloating, gassiness, and stomach pain. [13]

Assess Your IgE Levels with Everlywell

When the immune system wrongly recognizes a food protein as an allergen, it will disperse IgE to bind to cells throughout the body and initiate an allergic response. In the case of OAS, symptoms are typically isolated to the mouth, throat, tongue, and lips. However, other types of food allergies can impact the whole body.

The at-home Food Allergy Test from Everlywell will measure your body’s IgE reactivity to common food allergens, like almonds, cow’s milk, wheat, and more.

Stay a step ahead of seasonal allergies with support from Everlywell.

Are Food Allergies Genetic?

How Long Does a Food Allergy Reaction Last?

Common Food Allergy Symptoms


  1. Oral allergy syndrome. Children’s Hospital of Philadelphia. URL. Accessed May 5, 2023.
  2. Oral allergy syndrome. Cleveland Clinic. URL. Published August 11, 2023. Accessed May 5, 2023.
  3. Cross-reactivity defined. American College of Allergy, Asthma and Immunology. URL. Accessed May 5, 2023.
  4. Histamine. Cleveland Clinic. URL. Published March 28, 2023. Accessed May 5, 2023.
  5. Anaphylaxis. Cleveland Clinic. URL. Accessed May 5, 2023.
  6. Sussman G, Sussman A, Sussman D. Oral allergy syndrome. Canadian Medical Association Journal. URL. Published August 10, 2010. Accessed May 5, 2023.
  7. Bergmann K, Wolf H, Schnitker J. Effect of pollen-specific sublingual immunotherapy on oral allergy syndrome: an observational study. World Allergy Organization Journal. URL. Published May 15, 2008. Accessed May 5, 2023.
  8. Antihistamines. Cleveland Clinic. URL. Accessed May 5, 2023.
  9. Torborg H. Mayo Clinic Q and A: Reasons for developing allergies later in life not always clear. Mayo Clinic. URL. Published July 21, 2015. Accessed May 5, 2023.
  10. Food allergy. NHS. URL. Published January 5, 2023. Accessed May 5, 2023.
  11. Food allergy. Mayo Clinic. URL. Accessed May 5, 2023.
  12. Zhang S, Sicherer S, Berin M, Agyemang A. Pathophysiology of non-ige-mediated food allergy. ImmunoTargets and Therapy. URL. Published December 29, 2021. Accessed May 5, 2023.
  13. Food intolerance. NHS. URL. Published November 25, 2022. Accessed May 5, 2023.
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