What Is Oral Allergy Syndrome?

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Have you ever noticed a mild reaction soon after consuming certain types of foods? You may experience slight swelling of your lips, tongue, mouth, or throat; hives, an itchy or tingly mouth, or a scratchy, sore throat.  

If you have experienced these symptoms, you likely have oral allergy syndrome (OAS). This article will explain what causes it, what signs to look for, what you can do, and where to go for help.  

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What Is Oral Allergy Syndrome?

Oral allergy syndrome (OAS) is also known as pollen food allergy syndrome (PFAS) and is a heightened sensitivity reaction to various—often plant-based—foods. The syndrome commonly shows up in symptoms such as itching of the lips, mouth, and tongue.

Unlike a food allergy, OAS requires that you have prior exposure to a cross-reacting inhaled substance (or allergen) that you are sensitive to, rather than exposure to the specific food protein itself. Inhaled allergens come from trees, flowers, and dust mites.

Allergens are substances that can cause allergic reactions. Some people's immune systems will recognize an allergen as a foreign body and consider it to be dangerous. When this happens, the immune system mounts a defense using antibodies, to help protect against the allergen. This reaction is what causes allergy symptoms.

All Food-Related Allergies Are Not the Same

OAS and food allergies are not the same thing and have different symptoms. OAS symptoms are typically limited to areas around the mouth and throat, while food allergies can affect multiple parts of the body and can be life-threatening.

In addition to symptoms of OAS, other food allergies can cause difficulty breathing, abdominal pain, wheezing or trouble breathing, diarrhea, nausea or vomiting, dizziness, hoarse voice, fainting, and loss of consciousness. These symptoms can lead to a life-threatening condition known as anaphylaxis.

Signs and Symptoms

Usually, only the mouth, throat, and lips are affected in OAS. This condition usually occurs in adults; however, it can affect children, especially if they have allergic rhinitis (hay fever). The symptoms of children and adults are discussed below.

Childhood Signs

Children with OAS experience a reaction only in their lips, mouth, and throat. It appears in children who are allergic to mugwort and ragweed pollens, birch, or grass.

OAS occurs when the child eats a raw fruit, vegetable, or tree nut, and it causes a cross-reaction with the pollens mentioned above. Often, a child with OAS can eat the same food when cooked, baked, or canned, and it will not trigger a reaction.

It is essential to monitor any allergic reactions in your child in case their allergy may lead to something more serious. Reactions to watch for in your child can include:

  • An itching or tingling on the tongue or the roof of the mouth
  • Swollen or numb lips
  • A scratchy throat
  • Sneezing and nasal congestion

Adolescent and Adult Symptoms

As with children, if you are a person who suffers from hay fever due to a pollen allergy, your mouth or throat may become itchy after eating certain foods, such as an apple, banana, cantaloupe, or celery, and/or you may experience mild swelling of your tongue or lips. These symptoms are usually mild and disappear when you stop eating the food.

Causes of OAS

Allergic symptoms occur because your immune system is unable to tell the difference between the allergens found in trigger foods and the ones found in pollen. To your immune system, the allergens in both substances appear quite similar.

The immune response to the two allergens can make existing allergy symptoms worse and is referred to as a cross-reaction. In the case of pollen and food allergens, the resulting cross-reactivity causes OAS, also known as pollen fruit syndrome (PFS).

How Pollen Season Affects OAS

Pollen season typically begins in the spring and lasts until November. However, it can start as early as January in some parts of the southern United States. Some people are allergic to foods that trigger them only during the pollen season. After that, they can eat allergy-related foods without symptoms for the remainder of the year.

People with specific pollen allergies should avoid foods specific to their allergy type, especially during the pollen season. For example, if you have a birch tree allergy, you should avoid the following:

  • Almonds
  • Apples
  • Apricots
  • Carrots
  • Coriander
  • Celery
  • Cherries
  • Fennel

Similarly, if you have a grass allergy, you should avoid these foods:

  • Melons
  • Peaches
  • Tomatoes
  • Kiwi

With a ragweed allergy, you should take care not to eat: 

  • Bananas
  • Chamomile
  • Cucumbers
  • Echinacea
  • Melons, such as watermelons, cantaloupes, and honeydew
  • Sunflower seeds
  • Zucchini

Nut and Soy Considerations

Raw and roasted nuts can cause OAS, and you should pay special attention when eating them. Nut allergies can be very serious and you should always consult a healthcare professional if you have an allergic reaction to any type of tree nut.

Soy beverages such as soy milk also deserve special caution because they are associated with a higher risk of having a whole-body reaction that is more serious. People with OAS to soy should avoid drinking soy beverages because of this heightened risk.


Many people have OAS but don’t often know they do. For example, they have pollen allergies to certain trees and flowers and realize they cannot tolerate some foods; however, they do not connect the foods they can’t eat with their allergies.

People often find out they have OAS when their allergy tests are negative for foods but positive for grass, ragweed, or tree pollens, especially birch. 

When you see an allergist (an allergy specialist, usually a healthcare provider), they will recommend a skin or blood test to see what specific substances are causing your allergies. It is helpful to have a test at least once to establish what allergens trigger your allergies so you can take steps to avoid them.  


Most cases of OAS will not require medical treatment. However, if you have ever had symptoms that are concerning for a systemic allergic reaction such as difficulty breathing, chest tightness, throat symptoms such as swelling, hoarse voice, drooling or difficulty swallowing; vomiting, diarrhea, or loss of consciousness, you may need to carry a device that you can self-inject with epinephrine (using an Epi-Pen or a similar device) in case an emergency occurs.

Epinephrine is the most effective treatment for allergic reactions. You can obtain a prescription for this from your healthcare provider.

There are also over-the-counter antihistamines, such as Benadryl (diphenhydramine), to help relieve mild symptoms. Your local pharmacist can direct you to safe and effective treatments. Using a non-steroidal nasal spray can be effective in clearing nasal passages.

However, if you do see a healthcare provider, they may start you on prescription-strength antihistamines to treat itchy and runny nose and eyes. They can also prescribe a steroid nasal spray if you have more severe nasal passage congestion. Decongestants can be helpful, but since they are habit-forming, it's best to avoid using them daily.    

If your allergic rhinitis symptoms are bad enough, it may be recommended that you try allergy shots. However, allergy shots are not indicated for the sole use of OAS treatment.


The best way to prevent symptoms of OAS is to avoid the foods that cause allergic symptoms. You can peel the skin off an offending fruit or vegetable since most allergens are contained in the skin. You can also cook the food or microwave it for 15-30 seconds or more to eliminate most of the allergens that cause a reaction.

Antihistamine medications are often effective in reducing symptoms. It is best to take a non-sedating one if you need to be alert.


OAS is a common condition that affects people with pollen allergies. When they eat certain fresh fruits and vegetables, the allergens contained in those foods react with the allergens found in the pollens, and a cross-reaction occurs. This cross-reaction causes OAS.

Symptoms will usually go away if you stop eating the triggering food. You can also peel it or cook it to prevent symptoms. Antihistamines are a popular and effective treatment for many mild allergy symptoms.

A Word From Verywell

OAS can make you miserable. When you have some of the symptoms described in this article, it’s a good idea to see a healthcare provider, especially one who specializes in allergies, just to be on the safe side. They can discover what you are allergic to and suggest ways to avoid it. They can also share helpful ideas with you, or prescribe medications to relieve your uncomfortable symptoms and, most importantly, protect you from potentially serious harm. 

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Marybeth Gallagher, RN
Marybeth is a medical writer who explores all areas of scientific research and informs readers by demystifying technical jargon and simplifying statistics into an easily readable format.