You've had hay fever for years. You're used to the sneezing, the itchy eyes, the miserable June afternoons. But then one day you bite into an apple and your mouth starts to tingle. Your lips feel a little swollen. Your throat itches.
It feels unrelated. It isn't.
What is oral allergy syndrome?
Oral allergy syndrome (OAS) — also called pollen-food allergy syndrome — affects an estimated 2% of the population, but is significantly more common in hay fever sufferers. In some studies, up to 40% of people with birch pollen allergy also experience OAS.
The underlying mechanism is a case of mistaken identity. The proteins in certain raw fruits and vegetables are structurally similar to the proteins in pollen. Your immune system, already primed to attack pollen, recognises these food proteins as the same threat and triggers a reaction.
The result is typically a localised response in the mouth: tingling, itching, or mild swelling of the lips, mouth, and throat. It usually resolves within a few minutes.
Which pollens cross-react with which foods?
The cross-reactivity isn't random. It follows predictable patterns based on which pollen you're allergic to.
Birch pollen (the most common tree pollen trigger in the UK) is associated with reactions to:
- Apples, pears, peaches, cherries, plums, apricots
- Almonds, hazelnuts
- Raw carrots, celery, parsley
Grass pollen is associated with reactions to:
- Tomatoes, kiwi, watermelon, oranges
- Peanuts (though true peanut allergy is a separate, more serious condition)
Weed pollen (particularly mugwort) is associated with reactions to:
- Celery, carrots, fennel
- Various spices including coriander and aniseed
The proteins that trigger OAS are heat-sensitive. Cooking the offending food usually destroys the cross-reactive proteins entirely, which is why you may be able to eat cooked apples or tinned peaches without any problem at all.
Is it dangerous?
For the vast majority of people, OAS is uncomfortable but not dangerous. The reaction stays localised to the mouth and resolves quickly on its own. This is different from a true food allergy, where systemic reactions can occur.
However, there are exceptions. A small number of people experience more severe reactions, particularly with certain foods like celery or nuts. If you've ever experienced tightening of the throat, hives on your skin, or any difficulty breathing after eating, you should see a doctor rather than self-diagnose.
Pollen Level
Moderate
OAS reactions are typically mild and self-limiting, but they're worth tracking. Note which foods trigger symptoms and during which part of the pollen season — the pattern can reveal exactly which pollen is your primary trigger.
What to do about it
There's no treatment specifically for OAS, but there are practical ways to manage it:
- Cook or peel the food. Peeling often reduces the concentration of the cross-reactive proteins; cooking destroys them.
- Avoid the trigger foods during peak season. If raw apples cause problems in April but not in winter, your birch allergy is almost certainly the culprit. Simply avoiding the food when tree pollen is high can prevent symptoms entirely.
- Treat the underlying pollen allergy. Immunotherapy (desensitisation treatment) for birch pollen has been shown to reduce OAS reactions in many patients over time.
If you've started noticing odd reactions to foods you've eaten for years without issue, it's worth mentioning to your GP. OAS is widely underdiagnosed — many people assume their mouth tingling is a quirk rather than a recognised medical condition with a clear cause.