Oral Allergy Syndrome

Oral allergy syndrome (OAS) is a type of contact allergic reaction to vegetables, fruits and nuts. It most commonly affects your lips, mouth and throat.

Oral allergy syndrome usually isn’t serious. For most people, the reaction is limited to itching or minor swelling. Very few people with OAS experience a serious allergic reaction called anaphylaxis. Anaphylaxis may make it hard to breathe or cause dangerously low blood pressure. Call 911 or go to the emergency room if you have difficulty breathing, weakness, dizziness or other symptoms of anaphylaxis.

Oral allergy syndrome is sometimes called pollen-food allergy syndrome (PFAS). This is because it often happens when you have seasonal allergies to tree, grass or weed pollen.

Symptoms of oral allergy syndrome

Symptoms of oral allergy syndrome start quickly after you’ve eaten trigger foods. They 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

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. Which foods you react to depends on the other allergies you have.

That’s because your immune system mistakes proteins in these foods for something harmful. Many foods that cause OAS symptoms have proteins that are very similar to tree, grass or plant pollen. Your immune system mistakes food proteins for proteins in pollen that you’re allergic to.

You might hear this called cross-reactivity. 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 correct spot — even when it’s not.

List of OAS foods

If you’re allergic to certain pollens, you’re more likely to be allergic to related foods. Some people have symptoms with only one food. Others react to many 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

• 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
• Orange
• Potatoes
• Tomatoes

Ragweed pollen

• Bananas
• Cucumbers
• Melons
• Zucchini

Mugwort pollen

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

Complications

Complications of oral allergy syndrome are rare. Symptoms are usually minor and limited to your mouth or throat. This is because your stomach acid usually destroys the allergens before they can cause a reaction that affects your whole body. Rarely, OAS can lead to anaphylaxis, which can be life-threatening.

How doctors diagnose oral allergy syndrome

A healthcare provider (usually an allergist) diagnoses oral allergy syndrome based on your symptoms. They may confirm the diagnosis by doing allergy testing. This could include:

• Allergy skin tests
• Allergy blood test
• Food challenge tests

How is it treated?

There’s no specific treatment for oral allergy syndrome. Healthcare providers usually recommend you avoid foods you react to in raw forms.

Sometimes, peeling a fruit or microwaving it for at least 10 seconds may help you eat it without a reaction. In most cases, you don’t need to avoid cooked, baked, canned or processed forms of OAS foods. Heating fruits and vegetables changes the protein, so you don’t react anymore.

Symptoms are usually mild and go away quickly on their own. If you experience severe symptoms, then your provider may recommend you carry an epinephrine autoinjector (Auvi-Q®, EpiPen®). Epinephrine is the best treatment for severe allergic reactions.

When should I see my healthcare provider?

If you’re having reactions to foods — like they make your mouth itchy or your lips swell — talk to your healthcare provider. They can help you determine if it’s something serious that you need to treat. Avoid foods you might be allergic to until you talk to an allergist.

When should I go to the ER?

Go to the ER or call 911 (or your local emergency service number) if you have any signs of a severe allergic reaction, including:

• Swelling of your face, tongue or throat
• Trouble breathing or swallowing
• Signs of low blood pressure, like weakness or dizziness

Does oral allergy syndrome get better?

There’s no cure for oral allergy syndrome. But it can go away or get better for some people. Over time, you might get used to foods that once caused a reaction, or the reaction might become more tolerable.

Can OAS be prevented?

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: 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 reduce reactions to trigger foods.