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.
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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. 
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. 
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. 
In fact, it’s believed that between 47–70% of people with pollen allergies also experience OAS. 
So, why does this occur? Proteins in certain foods are similar to the proteins found in some allergenic plant materials.  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. 
This progression is what’s referred to as cross-reactivity. 
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. 
These antibodies can cross-react with proteins found in raw vegetables, fruits, and nuts, leading to a similar allergic reaction. 
That said, there are many potential cross-reactive foods that are similar to certain allergens and may trigger OAS symptoms: 
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.  Fortunately, less than 2% of people with OAS experience anaphylaxis, and food allergy symptoms are typically mild. 
An OAS allergic reaction can occur seconds or minutes after consuming a potential cross-reactive food. In other words, it develops quickly. 
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: 
Less common symptoms include: 
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. 
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. 
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:
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. 
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: 
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. 
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.  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. 
So, how exactly do pollen allergies develop?
Allergy development involves two phases: 
See related: Are Food Allergies Genetic?
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: 
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.  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: 
These types of food allergies can also develop into several food hypersensitivity syndromes, such as: 
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. 
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.
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