Oral Allergy Syndrome

Oral allergy syndrome (OAS) is an allergic reaction to certain foods, including fruits, vegetables and nuts. It most often happens if you have an allergy to trees, grass or other pollens (cross-reactivity). OAS makes your lips, mouth and throat itchy but rarely causes severe reactions. It’s usually managed by avoiding the foods that bother you.


What is oral allergy syndrome?

Oral allergy syndrome (OAS) is a type of food allergy to vegetables, fruits and nuts. It causes an allergic reaction usually limited to your lips, mouth and throat.

Because it’s the result of a cross-reaction to plant pollen (like tree, grass or weed pollen), it’s sometimes called pollen-food allergy syndrome (PFAS).


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Who does OAS affect?

Oral allergy syndrome mostly affects people who have allergies to tree, grass and weed pollen (seasonal allergies or allergic rhinitis). Children younger than 3 years old are unlikely to have OAS because it takes a few years of life to develop pollen allergies.

How common is oral allergy syndrome?

While we don’t know exactly how many people have oral allergy syndrome, it’s the most common food allergy in adults. Research estimates that between 47% and 70% of people with a pollen allergy have OAS.


Is oral allergy syndrome serious?

Oral allergy syndrome usually isn’t serious. For most people, the allergic reaction is limited to itching or minor swelling. Less than 2% of people with OAS experience a serious allergic reaction called anaphylaxis. Anaphylaxis makes it hard to breathe and can be life-threatening.

How does oral allergy syndrome affect my body?

An allergy is a reaction that your body has to something it thinks is harmful. In oral allergy syndrome, your immune system makes your lips and mouth swell up because it mistakes certain foods (trigger foods) for something harmful in your body. Your stomach acid usually destroys the proteins and the reaction doesn’t spread any further.


Symptoms and Causes

What are the symptoms of oral allergy syndrome?

Symptoms of oral allergy syndrome start quickly after you’ve eaten trigger foods, and include:

  • Itching, tingling or minor swelling of your lips, mouth, tongue or throat.
  • Bumps on your lips or mouth.

Less common symptoms affect other parts of your body:

  • Nausea.
  • Itching, redness or swelling of your skin when you touch certain raw foods.
  • Hives or a rash.
  • Trouble breathing (anaphylaxis) and other severe reactions are very rare.

What foods cause oral allergy syndrome?

Fruits, vegetables and nuts can cause oral allergy syndrome. They have proteins that look similar to pollen proteins, so your body reacts the same way it would to a tree, grass or plant allergen. It’s like a piece of a puzzle that’s just close enough to the right shape that you’re certain it’s in the right spot — even when it’s not. Which foods you react to depends on what other allergies you have.

List of OAS foods

If you’re allergic to certain pollens, you’re more likely to be allergic to related foods. You won’t be allergic to every food associated with a pollen, and sometimes you can be allergic to foods without being allergic to pollen.

Birch tree pollen

  • Herbs: Aniseed, caraway, coriander, fennel, parsley.
  • Legumes: Peanuts, soybeans.
  • Seed fruits: Avocados, apples, kiwis, pears.
  • Stone (pit) fruits: Apricots, cherries, peaches, plums.
  • Tree nuts: Almonds, hazelnuts.
  • Vegetables: Carrots, celery.

Grass pollen

  • Melons.
  • Oranges.
  • Potatoes.
  • Swiss chard.
  • Tomatoes.

Ragweed pollen

  • Artichokes.
  • Bananas.
  • Cucumbers.
  • Melons.
  • Zucchini.

Mugwort pollen

  • Garlic.
  • Herbs: Aniseed, caraway, coriander, fennel, parsley.
  • Mustard.
  • Peppers.
  • Vegetables: Cabbage, carrot, cauliflower, celery, broccoli, parsnip, onion.

Other oral allergies include berries, citrus fruits, figs, grapes, mangoes, pineapples and pomegranates.

Diagnosis and Tests

How is oral allergy syndrome diagnosed?

A healthcare provider (usually an allergist) diagnoses oral allergy syndrome by listening to your symptoms. They may confirm the diagnosis by doing allergy testing.

How do you test for oral allergy syndrome?

An allergist can use a skin test or food challenge test to confirm that you have oral allergy syndrome.

  • Allergy skin test: Your provider will lightly scratch your skin with a small applicator. Each scratch puts a small amount of an allergen (like tree pollen) on your skin. Your provider may test you for pollen allergies and for any foods that made you react. The skin test causes a hive to form if you react to an allergen.
  • Food challenge test: Your provider will give you increasing amounts of a certain food and watch you for signs of allergic reaction.

Management and Treatment

How is oral allergy syndrome treated?

There’s no specific treatment for oral allergy syndrome. If you have a reaction, it should go away on its own within about 30 minutes once you stop eating the trigger food.

Taking antihistamine allergy medication might help stop a reaction or keep it from getting worse, but mild symptoms usually go away more quickly than medications start to work.

What medications are used for oral allergy syndrome?

Medications your healthcare provider may prescribe or recommend for oral allergy syndrome include:

  • Antihistamines. Antihistamines block chemicals in your body that cause mild allergic reactions. You can get antihistamines in over-the-counter allergy pills, including diphenhydramine (Benadryl®), fexofenadine (Allegra®) and loratadine (Claritin®). You may have to see which works best for you.
  • Epinephrine. You inject yourself with epinephrine if you’re having a severe allergic reaction. It reduces swelling and opens your airways so you can breathe. Your allergist may prescribe epinephrine (Auvi-Q®, EpiPen®) if you’ve had a severe reaction in the past.

What can I eat if I have OAS?

You can still eat most foods if you have oral allergy syndrome. Most people with OAS have reactions to a few fruits, vegetables and nuts, but not all.

How do you fix oral allergy syndrome?

There’s not really a way to fix oral allergy syndrome, though some treatments might help prevent a reaction in the future. For some people, OAS gets better over time, or their reaction to certain foods is more tolerable.


How can I prevent oral allergy syndrome?

You can prevent oral allergy syndrome by not eating trigger foods. Other ways you might be able to prevent or reduce a reaction to trigger foods include:

  • Cooking your trigger foods: Heating fruits and vegetables changes the protein so you don’t react anymore. People with OAS can usually eat cooked foods, sauces and pasteurized juices.
  • Avoiding foods you’re allergic to at certain times of the year: Most people’s seasonal allergies are the worst in the spring, summer or fall. Your reaction to trigger foods might be worse when you’re also having seasonal allergies.
  • Treating your allergies proactively: Taking allergy medicines daily might help some people avoid reactions to trigger foods.
  • Getting allergy shots (immunotherapy): Allergy shots give you increasing doses of things you’re allergic to. This gets your body used to the allergens so you don’t react or have a minimal reaction to them. For some people, allergy shots might help oral allergy syndrome.

Outlook / Prognosis

What can I expect if I have oral allergy syndrome?

Oral allergy syndrome rarely causes serious allergic reactions. If the symptoms you get from a certain food bother you, you can expect to avoid the food.

Does oral allergy syndrome go away?

Although there’s no cure, oral allergy syndrome can go away for some people. Over time, you might get used to foods that once caused a reaction.

Living With

When should I see my healthcare provider?

If you’re having allergic reactions to foods, talk to your healthcare provider about any concerns you have. They can help you determine if it’s just an annoyance or something serious that you need to treat.

When should I go to the ER?

Go to the ER if you have any signs of a severe allergic reaction, including:

  • Face swelling.
  • Tongue swelling.
  • Trouble breathing or swallowing.

What questions should I ask my doctor?

  • How serious is my allergy?
  • What foods am I OK to eat?
  • Would any treatments or therapies help?
  • What signs of a severe reaction should I look for?

A note from Cleveland Clinic

Oral allergy syndrome is mostly an annoyance, but some people have serious reactions. Talk to your healthcare provider or an allergist if you have concerns about food allergies. You may still be able to eat the foods you love, or find alternatives that don’t leave you itching for relief.

Medically Reviewed

Last reviewed on 08/11/2022.

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