From why some people feel sick when they’re tired to what causes the strange jolting sensation you sometimes feel when you’re falling asleep, our bodies are home to a long list of weird and often fascinating phenomena.

But while some of these are more commonly known – for example, the fact that anxiety can lead to feelings of nausea – others remain mostly misunderstood.

One such phenomenon is oral allergy syndrome, also known as pollen food syndrome. It’s not a term many people have come across, but according to Allergy UK, about 2% of the UK population have oral allergy syndrome, and it primarily affects those who suffer from hay fever.  

But what is it, you ask? Well, let’s just say if you’ve ever suffered from an itching or stinging sensation in your mouth after eating certain fruits and vegetables, you might be more familiar with oral allergy syndrome than you realise.

To find out more, we asked Dr Helen Evans-Howells, a GP and allergy expert, to tell us all about oral allergy syndrome, including the key symptoms associated with it. 

What is oral allergy syndrome?

As you might expect, oral allergy syndrome is a type of food allergy. It occurs due to a cross reaction with pollen – but not because pollen is present in the fruits and vegetables an individual is eating.

“Oral allergy syndrome occurs because raw fruit, vegetables and some nuts (not cashew nuts, pistachios or brazil nuts) look to the body like pollen,” Dr Helen Evans-Howells explains. “The protein within these foods is very similar to a type of protein in polled called PR-10, which can trigger an allergic reaction.” 

What are the symptoms of oral allergy syndrome?

On top of an itchy mouth and tongue, oral allergy syndrome can produce a number of other symptoms depending on the severity of the reaction.

“Individuals affected by oral allergy syndrome may develop symptoms including itching within the mouth, lip swelling, an itchy throat or occasionally a rash around the mouth,” Dr Evans-Howells says.

Most people with oral allergy syndrome will experience mild symptoms, and they’ll typically appear 5-10 minutes after eating the food you’re allergic to. You can expect symptoms to dissipate around an hour after consumption.

In severe cases, nausea, vomiting and breathing difficulties can occur – if you have any kind of reaction, it’s worth seeking the advice of your GP.  

Who does oral allergy syndrome affect?

Because of its links with pollen, oral allergy syndrome is more common in people who also struggle with hay fever. However, whether you also suffer from oral allergy syndrome partly depends on the kind of pollen you’re sensitive to.

“Oral allergy syndrome is particularly common for those who have birch pollen allergies – up to 50% of people in this group have pollen food syndrome,” Dr Evans-Howells explains.

“However, it can also occur in those with grass pollen allergies or even weed allergies, as well as in those with dust mite allergies – these people can have a cross-reaction with shellfish.”

As to when oral allergy syndrome tends to emerge, it’s pretty random. “Pollen food syndrome can occur at any point and can change with time,” Dr Evans-Howells adds.

“Environmental allergies tend not to disappear with age but their severity can be different from year to year; the same can be said of oral allergy syndrome and individuals can find that they either react to more fruits and vegetables with time or things get better. It is not possible to predict.”  

What kinds of foods trigger oral allergy syndrome?

Oral allergy syndrome can be triggered by a range of different fruits, vegetables, seeds, spices and nuts. However, it most commonly occurs with fruits such as apples and cherries, Dr Evans-Howells says.

The type of plant you react to will typically depend on the kind of pollen you’re sensitive to, according to Allergy UK. For example, if you’re sensitive to tree pollen (typically birch or alder pollen), then you might react to fruits such as pears and strawberries. However, if you’re sensitive to grass pollen, kiwis may be an issue.

The key identifying factor among all oral allergy syndrome trigger foods is the fact that they are raw. “Individuals may find that raw apples and cherries will give them oral symptoms, but when these foods are cooked – such as in apple pie, apple juice, (which is heated and pasteurised) or cherry jam – the symptoms no longer occur.”

This is because the proteins in the food change shape when they’re cooked, and no longer appear to the body like pollen, preventing a reaction.

“This is a crucial point in someone’s medical history,” Dr Evans-Howells adds. “If an individual continues to react to a cooked fruit or vegetable, this would imply a ‘true’ allergy and not simply pollen food syndrome.” 

What’s the best way to manage oral allergy syndrome?

While you can’t get rid of oral allergy syndrome through treatment – Dr Evans-Howells explains that research indicates that, unlike hay fever, oral allergy syndrome does not seem to respond to immunotherapy – there are ways to manage it.

“Some individuals with pollen food syndrome will find that they are able to eat the fruits and vegetables that affect them without trouble outside of pollen season,” Dr Evans-Howells says. “Others may find that the foods can be tolerated if the fruits are peeled.”

She continues: “However, most patients will find that their symptoms are present no matter what the time of year, and we would generally advise therefore that these foods are avoided in their raw form.”

If you have to cut numerous fruits and vegetables out of your diet due to oral allergy syndrome, Dr Evans-Howells recommends meeting with a dietitian to ensure your nutritional needs are still being met.

“People who have pollen food syndrome should be aware that they don’t need to avoid all fruits and vegetables but only those which trigger symptoms,” she adds. 

When do you need to seek treatment for oral allergy syndrome?

Most people with oral allergy syndrome won’t need to seek treatment – although if you have any doubts, you should visit a specialist.

“For those with pollen food syndrome who were born and raised in the UK, the type of protein which they react to would be highly unlikely to ever trigger anaphylaxis, and these people do not usually require allergy testing,” Dr Evans-Howells says.

“Where there is ever doubt about the diagnosis, however (particularly if symptoms occur with nuts) or if there have been systemic symptoms – i.e., a widespread rash, vomiting or anaphylaxis – a referral to an allergy specialist should be made.”

For more information on pollen food syndrome, you can check out the ‘hayfever help’ course on Dr Evans-Howells website or visit Allergy UK. 

Images: Getty