Oral allergy syndrome: spot signs and find out what can help

11th May, 2022 • 8 min read

Itchy mouth or throat when you eat raw fruits, vegetables or nuts? These symptoms are both signs of oral allergy syndrome (OAS), sometimes called pollen food syndrome.

“Having this reaction might mean you feel anxious about having an allergic reaction to foods,” says

Dr Adiele Hoffman
, Clinical Content Reviewer. “You may avoid eating them and miss out on variety and health benefits, or you might worry about developing allergies to other foods - so it could put you off wanting to try different dishes or go to restaurants. But mostly, OAS symptoms are mild and there’s plenty you can do to get a handle on the condition.”

What is OAS?

OAS happens when you have an allergic reaction immediately after eating certain raw fruits, vegetables or nuts. Your allergy antibodies mistake certain proteins in these plant foods for pollen and this triggers a reaction, meaning you get itching in your mouth and throat, and possibly tingling and mild swelling.

Are OAS and food allergy the same thing?

OAS is a type of

food allergy
. The difference between OAS and other food allergies is that OAS is triggered by allergens in raw fruit, veg and nuts that are very similar to the allergens in pollen. Other foods, such as dairy and seafood, don’t cause OAS but can trigger different symptoms - so it’s important to know which type of allergy you have and how to treat it.

Which foods cause OAS?

With OAS, you can have a reaction to pretty much any raw fruit, vegetable or nut. But the most common trigger foods are apples, peaches, kiwis, hazelnuts and almonds. Most people with OAS find they get a reaction to 1 or 2 foods but you might find you develop reactions to more foods over time.

Who is most likely to get OAS?

It’s the most common type of food allergy in adults, although it can affect children too.

OAS is caused by a pollen allergy - the same allergy that causes hay fever symptoms like a runny nose and itchy eyes. So if you have

hay fever
, you're also more likely to have OAS, and the other way round. But you could have OAS and not get hay fever symptoms, or just get very mild ones.

Rarely, OAS can affect people with rubber latex allergy, rather than pollen, because the protein structure of latex is similar to the fruit pollen structure in certain foods, like mango and melon.

What can increase the risk of OAS?

More research is needed but scientists think these factors could be at play:

  • other conditions: apart from hay fever, people with allergic
    may also be at higher risk of developing OAS
  • sensitisation: this is when your immune system learns to react to certain allergens. Sensitisation to tree pollens is linked with OAS, especially birch tree pollen - 50-75% of people with birch tree pollen allergy also get OAS

What are the symptoms of OAS?

  • for most people, symptoms are mild and can include an itchy, tingling mouth and throat, and sometimes lips. You might also get a slightly swollen mouth, throat or lips. These symptoms typically flare up just a few minutes after eating the food and they usually settle down within an hour
  • some people occasionally get itching, redness or slightly swollen hands when peeling raw fruit or veg
  • less common symptoms include nausea, vomiting and very rarely – in just 1.7% of reactions – severe allergic reaction (anaphylaxis) with breathing difficulties

Even if your symptoms are mild, OAS can feel worrying, especially the first time it happens. The good news is there’s plenty you can do to manage it.

How to manage OAS

First, identify the food that triggers a reaction - often it will be obvious but if not, a

food and symptom diary
could help. Once you’ve pinpointed the food, the golden rule is to avoid eating it raw. There are some other useful tips that might also help.

Prepare food yourself

  • see if cooking or microwaving the food, or eating it in canned form, makes any difference – heat affects the proteins in food and deactivates the allergens
  • but be aware lightly cooked foods – for example, stir-fried vegetables – can still cause a reaction
  • try removing the skins of fruit and veg - this can sometimes help as the reaction-causing proteins are often found in the skin

Choose wisely when you eat out or order in

  • when you’re eating out, ordering a takeaway or shopping for food, do your research - check labels and quiz staff about ingredients
  • remember hidden sources, such as fresh fruit smoothies, vegetable juices, mixed salads and fruit salads - it may not always be obvious they contain the foods you react to, so check ingredients carefully

Make the most of your medicines

  • keep
    with you to treat an allergic reaction if it doesn’t get better on its own
  • if you’ve had a severe reaction or anaphylaxis in the past and you’ve been prescribed an
    adrenaline auto-injector
    , it’s essential to carry this with you all the time
  • if you have prescription medicine for other allergies, such as asthma or hay fever, it’s important to take it as it can help keep your OAS under control too

How to treat a mild allergic reaction

Remember that in most cases, OAS symptoms are mild and should settle down within an hour. Here’s what can help:

  • stop eating the food immediately
  • rinse your mouth with water
  • take a dose of non-sedating
    as this can help relieve itching. If symptoms aren’t improving after taking antihistamines, you might need more treatment so call your doctor for advice

How to treat a severe allergic reaction

It’s unlikely you’ll have a severe allergic reaction (

) but if it does happen, it may be life-threatening. Seek emergency medical help immediately if:

  • you’re having breathing difficulties, including wheezing or fast or shallow breathing
  • you have clammy skin
  • you feel faint
  • you turn pale or floppy

If you have an adrenaline auto-injector, use it as soon as you think you might be having a severe allergic reaction and call an ambulance immediately.

Reducing your risk of a severe allergic reaction

There are a few things that can dial up your chance of a severe reaction:

  • eating a large amount of the trigger food in a short space of time
  • having allergies to lots of different plant-based foods
  • poorly managed asthma - if you have asthma, making sure you take your medicines properly, as prescribed by your doctor, can reduce your risk of a severe OAS reaction
  • eating the food along with exercising or taking certain medicines may raise risk of a severe reaction, research shows

When to see a doctor

Try our

Smart Symptom Checker
– designed by doctors to help you learn more about your symptoms. If you think you might have OAS, speak to your doctor, who can advise you on next steps.

How OAS is diagnosed

Your doctor might be able to diagnose OAS by asking you a few questions. But if things aren’t clear-cut, you might need to see an allergy specialist. To find out what’s going on, the specialist might recommend skin testing or a food challenge – where you eat a food or put a drop of liquid on your skin and they check your reaction.

Get the most from your appointment

  • keep a food diary and take it to your appointment to help you and your doctor see a pattern
  • know about any family history of allergies in advance, plus any other allergies you have

How is OAS treated?

You should be able to live with OAS by following the tips above. But if you’re at risk of severe reactions, your doctor might prescribe adrenaline auto-injector devices (AAIs), or adrenaline pens. These contain adrenaline (also known as epinephrine), which you inject into your thigh muscle as soon as a suspected severe reaction starts – the medication works to stop the reaction becoming life-threatening. Your doctor will take you through exactly how and when to use it.

Your health question answered

Will my OAS ever go away?

“So far, there’s no proven cure for OAS, but knowing your food triggers means you can prevent symptoms. Doctors might consider

if you have very severe symptoms. This is sometimes used for people with pollen allergies that cause hay fever or asthma, and works by giving you small amounts of the allergen either by injection or orally to desensitise you to it. But although it’s been shown to work in asthma and hay fever, studies so far haven’t proven whether it works or not for OAS.”– Dr Adiele Hoffman

Doctor’s tip

“As we often diagnose OAS based on your symptoms alone, food and symptom diaries can be really helpful to identify which foods cause a reaction in you. Try using the Healthily

Smart Symptom Checker
to figure out what your triggers are.” – Dr Adiele Hoffman

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.