What is oral allergy syndrome?

What is oral allergy syndrome? It could give this woman a tingly mouth if she has hay fever and eats her slice of watermelon

People with hay fever can get a mild reaction in their mouth, lips or throat when they eat certain foods. It’s called oral allergy syndrome (OAS). And it’s usually more bothersome than serious.

Oral allergy syndrome happens because of cross-reactivity. It isn’t a primary allergy. Rather, proteins in certain foods look a lot like those in the pollen you’re allergic to. Your immune system struggles to tell the difference and reacts to the food too. Other names for it are pollen food syndrome (PFS) and pollen-food allergy syndrome (PFAS). It can also happen to people who are only sensitized to pollen and haven’t developed an allergy.

Let’s find out more about this common condition – how to identify, diagnose and treat it. And why you might develop these symptoms.

How does oral allergy syndrome start?

First off, you need to be sensitized or allergic to pollen. It could be grass, ragweed or mugwort pollen, or a tree like alder or birch.

Pollen allergy happens because your immune system makes a mistake. It thinks pollen, the fine dust that plants release, is dangerous to you. You meet pollen for the first time and your immune system makes IgE antibodies (immunoglobulin E). Now you're sensitized. The antibodies are always on alert for your trigger, ready to defend you next time you meet it. What they're looking for are particular proteins in the pollen. Proteins that happen to be very similar to those in certain foods.

Oral allergy syndrome = a case of mistaken identity

Proteins are not just part of a balanced diet. They’re the building blocks of all living things from the tiniest mold to the blue whale. Protein families share similar characteristics and functions. There are thousands of families but only a handful seem to be the cause of the majority of allergies.

Your body may be on the lookout for a protein in grass pollen and react to one like it in certain raw fruits like peach. It’s a bit like someone mistaking you for your younger brother or sister on the phone. The allergenic proteins in grass pollen and peach are related. And that confuses your immune system.

How common is pollen food syndrome?

It wouldn't be surprising for someone with hay fever (allergic rhinitis) to get pollen-food allergy symptoms too. One study suggests pollen-food allergy syndrome could affect up to 70% of people with pollen allergies. That figure varies widely because the data comes from different places. Different plants grow locally so the levels of the more problematic pollen types are different too.

Ragweed allergy

Ragweed growing on the edge of a field. The pollen is a major cause of hay fever and cross-reacts with some tree pollens too

But it does seem as if more adults are affected by pollen food syndrome than children. Teens and young adults may develop symptoms after happily eating the fruit or vegetables for years.

Which plants are linked to oral allergy syndrome?

Some types of tree, weed and grass pollens are more likely to give you an oral allergic reaction. These include:

  • Pollens from trees, grasses or weeds
  • Waste particles from house dust mites
  • Molds
  • Certain foods such as nuts, dairy, shellfish
  • Pet dander
  • Insect stings

Juniper pollen allergy can also give you a tingly mouth. So can ash, although it’s rare.

People with seasonal allergies to mold may get a mild allergic reaction when they eat mushrooms, yeast or spinach. This is also oral allergy syndrome.

Which foods are linked to oral allergy syndrome?

They mostly come from the fresh fruit and vegetable aisles of the supermarket. But there are nuts, legumes and spices on the list too. Which foods you react to will depend on your particular pollen trigger. For instance, if you’re allergic to ragweed pollen you might get symptoms from eating melon.

Tree pollen allergy to alder (or sensitization) can make you react when you eat apples. It could be symptoms occur only with a certain type of apple. This is because the proteins can vary within a species of fruit or veg. One type but not resemble the pollen protein as closely.

Common pollen food cross-reactions


Apple | apricot | cherry | peach | pear | plum | carrot | celery | parsley | peanut | soybean | almond | hazelnut


Apple | banana | tomato

Timothy and orchard grass

Peach | watermelon | orange | tomato | white potato


Cantaloupe and honeydew melon | watermelon | banana | cucumber | white potato | zucchini | sunflower seeds


Bell pepper | broccoli | cabbage | cauliflower | chard | garlic | onion | parsley | aniseed | caraway | coriander | fennel | black pepper


Pineapple | horseradish


Apple | cherry | peach | pear | parsley | celery | almond | hazelnut

Symptoms of oral allergy syndrome

Your body reacts to the food in a similar way it would to pollen. You breathe in the tiny grains and that causes local inflammation in your nose and airways. Pollen landing on your eyes makes them itch and water. The immune response when you eat the raw fruits or vegetables linked to your pollen trigger also sets off a local reaction. That is, around your mouth and usually within five to 10 minutes.

It’s called oral allergy syndrome because it involves a range of symptoms and signs. These usually appear in a cluster and include an itchy swollen mouth, scratchy throat and swollen lips and tongue. Some people get hives on their mouth and itchy ears too.

See a doctor if peanuts, soybeans, almonds or hazelnuts give you an itchy mouth or throat. That may also be an early warning of a dangerous food allergy that can affect your whole body.

Can oral allergy syndrome cause severe reactions?

You don’t usually get severe systemic symptoms with pollen food allergy syndrome. And the reaction tends to calm down quite quickly. But there are factors that can aggravate your response.

For instance, taking antacids for indigestion or heartburn. This everyday medication can change protein structure to make reactions more likely. Exercising before eating can cause more severe reactions in some people. So can eating (or drinking) a lot of the problem food in a short space of time. More severe symptoms – a significant throat discomfort, difficulty swallowing or even difficulty breathing – are your signal to get immediate help.

Food containers on a shelf

Managing food allergies

Other respiratory allergies linked to food

It's rare but there is a link between allergy to cat dander and a reaction to pork. You may get an itchy mouth while still eating. Otherwise symptoms, like stomach cramps, tend to start within 30-45 minutes.

Pork-cat syndrome is known to behave more like a main IgE food allergy and it can be life-threatening.

Oral allergy syndrome and food allergy: What’s the difference?

Food allergy symptoms can start after exposure to even a tiny amount of your allergen. The reaction may affect different parts of the body:

You might experience an allergic reaction caused by spores from mold and fungi. Spores are widespread in the air we breathe. Spores come from rotting organic matter and their development increases in warm and humid conditions.

  • Tingling or itching in the mouth
  • A raised, itchy red rash (hives) – sometimes the skin can turn red and itchy but not raised
  • Swelling of the face, mouth, throat or other parts of the body
  • Difficulty swallowing
  • Wheezing or shortness of breath
  • Feeling dizzy and lightheaded
  • Feeling sick (nausea) or vomiting
  • Abdominal pain or diarrhea

Severe food allergies can also cause anaphylactic shock which is a medical emergency. In oral allergy syndrome or pollen food syndrome, the tingling usually calms down once you swallow the trigger foods. Or spit them out. So systemic reactions and more severe symptoms are less usual.

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House dust mite allergy

Dust mite allergyis another common form of allergy. Dust mites are found all over the world, living in our homes and causing some of us to cough and sneeze. Dust mite allergy isn’t a reaction to the mites themselves, but to their waste and shed skin.

Pet allergy

Furry or hairy domestic animals produce allergens that can cause allergies. We’re talking cats, dogs, horses, rabbits and guinea-pigs and suchlike. It’s their dander that triggers the allergic reaction. Dander is flakes of their dead skin, fur or hair. Their urine and saliva also contain allergens that may cause a reaction.

Oral allergy syndrome and food intolerance: What’s the difference?

Pollen food allergy syndrome involves an immune response. Food intolerance doesn’t. Instead it means your body has difficulty digesting certain foods. There are no pollen proteins responsible for feeling unwell when you eat. Symptoms tend to be mild and mostly in the gut.

Getting a diagnosis of oral allergy syndrome

A diagnosis is the first step to managing symptoms, both food-related and hay fever. Maybe you've never been to the allergy clinic before despite always reaching for paper tissues at certain times of year. If so, pollen allergy can be part of the conversation with your healthcare provider.

They may ask you to keep a record of all your symptoms. It's important to know what you ate before you got that itchy mouth. Also whether it happens at the same time of year as your hay fever. Or if it's worse then. And whether only raw food gives you symptoms or if it happens when it's cooked or heat-treated too. That's less usual with oral allergy syndrome.

There’s no specific test for pollen food syndrome. But there are ways to narrow down what could be causing your symptoms.

Quote Image

It’s usually raw foods that cause symptoms. Particularly concentrated versions like smoothies or fresh juice. So learn to love cooked or heat-treated fruit and vegetables.

Oral allergy syndrome: Tests and challenges

  • Skin prick tests: This type of test can check for allergic reactions to pollen and for pollen food allergy syndrome. The latter is likely to involve raw fruit and veg. Heat used in the preparation of allergen extracts can alter the proteins and affect test results.
  • Oral food challenge: One reason to suggest an oral food challenge is if your skin prick test was inconclusive. You start by eating very small amounts of raw fruits or vegetables and build up gradually. Medical staff will watch for any reactions.
  • Component blood test: Foods often contain more than one allergenic protein. This type of allergy blood test can look for antibodies to the proteins most associated with cross-reactivity.

Managing oral allergy syndrome

Allergy medicines aren’t generally necessary for oral allergy syndrome. Symptoms tend to settle down in 30 minutes to an hour. You can help them along by rinsing your mouth out with a glass of water. Your healthcare provider can tell you more.

In the meantime, here are some ideas that may help you manage your oral allergy syndrome.

3 ways to enjoy your 5-a-day with oral allergy syndrome

Your pollen food syndrome symptoms may flare-up during hay fever season, whenever that is for you. So pay extra attention to what you eat then. The good news is you may not have to give up those healthy plant foods altogether.

  1. Cook your problem food: It’s usually raw foods that cause symptoms. Particularly concentrated versions like smoothies or fresh juice. But heat changes the shape of the proteins that usually cause OAS. Your immune system is less likely to confuse them with pollen proteins. So you may be able to tolerate them better. Learn to love cooked or heat-treated fruit and vegetables. That includes pasteurized juice and tinned or dried fruit.
  2. Peel it: Removing the skin and only eating the flesh of the fresh fruits or vegetables can make a difference too. But wear gloves or ask someone else to do it as contact with the skin can cause symptoms. Peeling fruit and veg under running water may stop a mist of allergenic particles irritating your nose and eyes.
  3. Get creative: Experiment with unfamiliar fruit and vegetables that don't give you symptoms. Make simple substitutions. For instance, avocado is good for thickening smoothies if you can’t use bananas. Or try pumpkin in your carrot cake recipe. A new cookbook is a good way to turn a change of ingredients into a gourmet adventure.
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