Oral Allergy Syndrome – What to know & Avoid

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Everything you need to know about oral allergy syndrome, including symptoms, diagnosis, foods to avoid, and more! 

This article walks you through all aspects of oral allergy syndrome, including symptoms, what foods to avoid, getting a diagnosis, treatment, and how best to manage your pollen food allergy syndrome. 

birch trees in a forest with questions about oas on top

What is Oral Allergy Syndrome

Oral Allergy Syndrome (OAS), and also known as Pollen-Food Allergy Syndrome (PFAS) or birch pollen allergy, is a hypersensitivity reaction to fruits, vegetables, and tree nuts when eaten in their raw form. 

It is a secondary allergy that develops in response to the similar proteins structure to a primary allergy. This primary allergy is usually to alder tree pollen, birch tree pollen, dust mites, grass pollen, or weed pollen. 

In other words, your immune system thinks that foods you are not allergic to are too similar to foods you are allergic to. And then it causes a reaction “just to be safe” in case you are allergic. Think of it like your immune system being a hyperactive security team. 

Unlike seasonal allergies, OAS happens when you eat the raw food. However, because OAS starts from a pollen allergy, your symptoms can get worse during hay fever season. 

OAS is a rather common condition that affects upward of 10% of the global population.  

Oral allergy syndrome can be misdiagnosed as a food allergy. However, the reactions are the same and can be life-threatening, so I say to treat it with the same care and respect that you treat other allergies. 


Interestingly, OAS does not usually appear in young children under the age of 3. Older children, teens, young adults, and adults who have been eating and enjoying these foods for years suddenly develop these reactions. 

It primarily affects people who have allergies to pollen, specifically birch pollen, grass pollen, and weed pollen (ragweed and mugwort in particular). However, you do not need to have these allergies to have OAS. Everyone’s immune system is unique and reacts to different things differently. 

People who have other food allergens do not seem to be more affected than those who don’t.

symptoms of oral allergy syndrome on a white box with an image of trees


Eating fresh raw fruits, raw vegetables, and raw nuts or seeds can trigger OAS. Some people are only reactive to one or two foods, while others are reactive to a whole list of foods. 

These reactions usually happen within the first 10 minutes after touching or eating the food. You may also notice it during food preparation, such as chopping up fruit and vegetables. 

Some people are so sensitive that they can have severe allergic reactions to the food particles in the air, causing eye irritation. 

The most common foods to trigger a reaction are fresh fruits and raw nuts including: Apples, peaches, kiwi, hazelnuts, and almonds. Please see the list below for a more complete list of triggers. 

A list of the most common allergy symptoms includes: 

  • Itching and swelling of the lips, tongue, inside of the mouth, ears, and/or throat
  • Skin irritation from where the food touched the skin
  • Sneezing
  • Runny nose
  • Irritation to the eyes, watery eyes

More rare systemic symptoms of OAS include: 

  • Nausea
  • Vomiting
  • Asthma attacks
  • Anaphylactic shock 

You are more likely to develop a severe reaction if you have one or more of the following:

  • Consumed a large amount of the allergen in a short time period (drinking soy milk, drinking juice, etc)
  • Having allergies to many different plant based foods
  • Having uncontrolled asthma

Anaphylactic Symptoms 

For some people, a life-threatening reaction known as an anaphylactic reaction may occur after consuming, touching, or even smelling one of their trigger foods. If this happens, please call 911 or your local emergency number immediately. Signs and symptoms of this include:

  • Swelling and tightening of the throat
  • Difficulty breathing
  • Chest pain or tightness
  • Trouble swallowing
  • Dizziness or fainting
  • Change of normal coloring of the skin in the mucous membranes (inner lips, gums, around hte eyes, and nail beds)
    • Light skin, check for signs of a dark blue tint in the mucous membranes
    • Medium skin, check for signs of a gray-green tint in the mucous membranes
    • Dark skin, check for signs of a gray or white tint in the mucous membranes 


An allergy doctor can officially diagnosis OAS. They will start with taking the patient’s history, possible use of a skin prick test, oral food challenges, and elimination diets. 

First, the doctor needs to determine which primary allergy is causing the OAS to occur or if you have a true food allergy. There are 4 ways to clinically determine if someone has a food allergy. They are: 

Skin Prick Tests

A low risk method where a small amount of the suspected allergen is pricked under the skin. All reactions, if any, are monitored by a health professional. Reactions usually range from a light rash to hives. The severity of the allergy is determined by the strength of the skin reaction. 

Note! If you have dermatographia urticaria the skin prick testing will not give you accurate results.

Blood Test

A low risk method where blood is drawn and then tested in a lab to measure the amount of IgE antibodies that the immune system has deployed in response to food-based [proteins. 

Component Test

This is a low risk method where blood is drawn and tested in a lab to measure a response of a reaction to nuts. 

Oral Food Challenge

This is the gold standard for food allergy and food sensitivity testing. A suspected food (or foods) are removed from the diet for a period of 2 to 4 weeks before being reintroduced. The strength of a reaction, if any, helps to determine what food allergies are present. This is only to be done in the presence of a doctor or medical professional as sever reactions can occur. 

A patient is considered at risk for an anaphylactic reaction if the patient has experienced a reaction beyond the mouth area.  

Some research has found that up to 9% of people with OAS have systemic (whole body) symptoms and up to 2% have anaphylactic reactions. Make sure you speak with your doctor to know if you are at risk and if you should carry an epinephrine auto-injector to treat potential severe reactions. 

green box with text explaining about OAS with an image of birch trees


Avoiding the foods that trigger a reaction is the best way to manage oral allergy syndrome. You do not need to avoid foods that do not cause any symptoms. 

When cooking these foods, you can reduce your risk of a reaction by wearing food safe gloves to handle the food. You can also peel fruits and vegetables under water to reduce the risk of eye irritation. If eye irritation is a major problem, consider wearing safety goggles while prepping foods that trigger your OAS. 

Finally, it is important to talk with your doctor about taking medication to help with your asthma and other allergies. This will also help control the symptoms of your pollen food syndrome. 

If you have experienced any difficulty breathing or other symptoms of anaphylaxis, you should contact your doctor immediately. A new food trigger can happen at any point so you always need to be aware of your body and how it reacts to foods. 

collage of the most common triggers for OAS including apples, peaches, kiwi, hazelnuts, and almonds


The majority of OAS reactions are mild and stopping eating or drinking of the trigger is enough to stop the reaction. Rinsing your mouth out with water can help speed the process up. The symptoms should diminish within one hour after stopping eating or touching the foods. 

Following your doctor’s orders, you can also take an antihistamine to help speed up the process of recovering. 

If you have symptoms after one hour, after taking an antihistamine, or are having trouble breathing at any point, you should seek emergency medical care immediately. 

If your OAS is triggered by inhaled environmental allergens, such as tree pollen or dust mites, treating the allergy can help relieve symptoms. This can include things like taking antihistamines or seasonal allergy shots. 

Cooking foods

When you cook the foods that are common for triggering OAS, you are less likely to have a reaction to them. The cooking process changes the structure of food. Cooking changes the proteins, distorting them. Then, the immune system no longer recognizes the proteins are being similar. Therefore, no reaction. 

Most people with OAS can tolerate well-cooked fruits and vegetables. Lightly cooked vegetables, for example a stir-fry, have been known to cause reactions. 

Remember, OAS occurs when you eat or are exposed to the RAW fruits, vegetables, nuts, and seeds. The proteins in the food are changed during the cooking process and potentially safe for you to eat.

This is why OAS is not a true food allergy because after cooking you can eat the food. With a true food allergy, it does not matter if the food is cooked or not.

Again, this is all subject to you, your body, and your unique needs to discuss with your doctor.

Foods to Avoid 

OAS is unique in that the list of food triggers will be different for everyone. Not everyone has the same pollen allergies and each person’s body will react in different ways to the different foods. Therefore, this list is NOT a list of foods you must avoid, but rather, a list of foods that MIGHT be possible triggers. 

That means that you must always be aware that these foods can cause an issue at any point in your life. It does not mean you must avoid these foods if you have never had an issue before. Only remove them from your diet if they trigger a reaction. 

Birch pollen: Apple, almond, carrot, celery, cherry, hazelnut, kiwi, peach, pear, plum, strawberry, apricot, coriander/cilantro, nectarine, parsley, bean sprouts, green pepper, potato, soy beans, tomato, parsnips, peas, brasil nut, walnut 

Grass pollen: Celery, melons, oranges, peaches, tomato, kiwi, watermelon, dates, potatoes, swiss chard, wheat, peas, peanuts

Weed (ragweed and mugwort) pollen: Banana, cucumber, melons, sunflower seeds, zucchini, apple, orange, peach, tomato, watermelon, celery, carrot, green pepper, onion, sunflower seed, aniseed, celery salt, mustard, coriander, fennel, parsley 

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