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.
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).
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
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.
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.
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.
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 of oral allergy syndrome start quickly after you’ve eaten trigger foods, and include:
Less common symptoms affect other parts of your body:
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.
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
Other oral allergies include berries, citrus fruits, figs, grapes, mangoes, pineapples and pomegranates.
A healthcare provider (usually an allergist) diagnoses oral allergy syndrome by listening to your symptoms. They may confirm the diagnosis by doing allergy testing.
An allergist can use a skin test or food challenge test to confirm that you have oral allergy syndrome.
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.
Medications your healthcare provider may prescribe or recommend for oral allergy syndrome include:
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.
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.
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:
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.
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.
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.
Go to the ER if you have any signs of a severe allergic reaction, including:
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.
Last reviewed by a Cleveland Clinic medical professional on 08/11/2022.
Learn more about our editorial process.