Oral Allergy Syndrome (OAS)
Symptoms, Causes & Allergy Testing in London
Oral Allergy Syndrome (OAS), also known as Pollen Food Syndrome (PFS), is a common cross-reactive food allergy seen in people with birch, grass and mugwort pollen allergy.
At the London Allergy and Immunology Centre, we provide specialist assessment, diagnosis and management for children and adults with symptoms suggestive of oral allergy syndrome, using detailed clinical history, targeted allergy testing and personalised treatment plans.
What is Oral Allergy Syndrome?
Oral allergy syndrome is a cross-reactive allergy that happens when the immune system recognises proteins in certain raw fruits, vegetables, nuts or legumes as similar to pollen allergens.
This is why many people with hay fever notice itching or tingling in the mouth after eating foods such as apple, carrot, hazelnut, peach or melon.
In most cases, symptoms are mild and limited to the lips, mouth, tongue and throat, but more significant reactions can occasionally occur.
Birch pollen allergy is one of the most common causes of oral allergy syndrome in the UK.
Common Symptoms of Oral Allergy Syndrome
Symptoms usually begin within minutes of eating raw plant foods. Common symptoms include:
✔ Itching or tingling of the lips, mouth, tongue or throat
✔ Mild swelling inside the mouth or throat
✔ A scratchy or uncomfortable throat
✔ Occasional lip irritation or symptoms while peeling or preparing foods
✔ Nausea or mild discomfort in some patients
Although anaphylaxis is uncommon in classic oral allergy syndrome, patients with wheeze, breathing difficulty, collapse, widespread hives or more severe reactions need urgent specialist assessment.
Pollen and Food Cross-Reactions
Symptoms occur because certain food proteins share structural similarities with pollen allergens.
| Pollen sensitisation | Common cross-reactive foods |
|---|---|
| Birch pollen | Apple, carrot, hazelnut, peach, pear, celery, soya, kiwi |
| Grass pollen | Melon, tomato, orange, peanut in selected patients |
| Ragweed pollen | Banana, cucumber, courgette, melon, sunflower seeds |
| Mugwort pollen | Celery, carrot, spices, melon |
Why Cooking Often Prevents Symptoms
Many of the proteins involved in pollen food syndrome, particularly PR-10 proteins, are heat-labile.
✔ Cooking or microwaving often reduces allergenicity
✔ Peeling fruit may reduce exposure to allergenic proteins near the skin
✔ Processed or canned versions are often better tolerated than raw foods
The Role of Bet v 1 in Oral Allergy Syndrome
Bet v 1 is the major birch pollen allergen and one of the key drivers of pollen food syndrome linked to birch sensitisation.
It belongs to the PR-10 protein family. Similar PR-10 proteins in foods can trigger cross-reactive oral symptoms.
Component testing can help identify sensitisation to Bet v 1 and other clinically relevant allergen molecules.
Examples of cross-reactive proteins include:
✔ Mal d 1 – apple
✔ Pru p 1 – peach
✔ Cor a 1 – hazelnut
✔ Ara h 8 – peanut
✔ Gly m 4 – soya
✔ Api g 1 – celery
✔ Act d 8 – kiwi
✔ Dau c 1 – carrot
Where symptoms are more severe or the clinical picture is unclear, additional components such as Pru p 3 may be relevant because lipid transfer proteins are associated with a higher risk of systemic reactions than classic PR-10-mediated oral allergy syndrome.
Diagnosis and Allergy Testing for Oral Allergy Syndrome
At the South London Allergy Clinic, part of the London Allergy and Immunology Centre, diagnosis starts with an allergy-focused clinical history followed by targeted testing where needed.
Step 1 – Detailed Clinical Assessment
✔ Timing of symptoms after eating raw foods
✔ History of hay fever or pollen allergy
✔ Foods that trigger reactions
✔ Tolerance to cooked, peeled or processed forms
✔ Any systemic symptoms suggesting primary food allergy
Step 2 – Allergy Testing
✔ Skin prick testing, including fresh food testing where appropriate
✔ Specific IgE blood testing to relevant pollens and foods
✔ Component-resolved diagnostics for selected cases
✔ Assessment of components such as Bet v 1 or Pru p 3 when clinically useful
Management of Oral Allergy Syndrome
Most patients can manage oral allergy syndrome safely with practical dietary adjustments and specialist advice.
Avoid Trigger Foods
✔ Avoid raw foods that reliably trigger symptoms
✔ Be particularly cautious during the pollen season
Modify Food Preparation
✔ Cook fruits or vegetables where possible
✔ Peel fruits if the skin seems to worsen symptoms
✔ Try processed or canned forms if suitable
Medication
✔ Non-sedating antihistamines may help mild symptoms
✔ Patients with more significant reactions may require individualised advice
Allergy Immunotherapy
✔ In selected patients, pollen immunotherapy may improve hay fever symptoms
✔ Some patients also notice improvement in oral allergy syndrome symptoms
When to Seek Specialist Allergy Care
Consult an allergy specialist if:
✔ Symptoms persist despite avoiding trigger foods
✔ You are unsure whether the problem is oral allergy syndrome or true food allergy
✔ Reactions involve breathing difficulty, wheeze, collapse or widespread rash
✔ Nut allergy or lipid transfer protein sensitisation is suspected
✔ Your child is avoiding multiple foods and needs a clear diagnosis
Allergy Testing for Oral Allergy Syndrome in London
The London Allergy and Immunology Centre provides comprehensive diagnosis and treatment planning for patients with suspected oral allergy syndrome, pollen food syndrome and cross-reactive food allergy.
✔ Fresh food skin prick testing where appropriate
✔ Specific IgE and component testing
✔ Personalised management plans
✔ Assessment for hay fever treatment and pollen immunotherapy
✔ Remote consultations for patients across the UK
Frequently Asked Questions
Can oral allergy syndrome occur in children?
Yes. It can occur in children as well as adults, especially in those with seasonal allergic rhinitis, although symptoms may be overlooked or confused with dislike of certain raw foods.
Are cooked foods usually safe?
Often, yes. Many patients tolerate cooked, peeled or processed foods because heat can denature the proteins involved in classic pollen food syndrome.
Is oral allergy syndrome related to latex allergy?
Sometimes. A separate latex-fruit syndrome can involve foods such as banana, avocado and kiwi, so the pattern of symptoms matters and should be assessed clinically.
Do I need an adrenaline auto-injector?
Not everyone with oral allergy syndrome needs one. The decision depends on your reaction history, the foods involved and whether testing suggests a risk beyond classic mild oral symptoms.
Key Takeaways
✔ Oral allergy syndrome is common in people with pollen allergy
✔ Symptoms usually affect the mouth and throat after raw plant foods
✔ Birch pollen and Bet v 1 are major drivers of classic pollen food syndrome
✔ Cooking often reduces or prevents symptoms
✔ Component testing can help distinguish cross-reactive syndrome from primary food allergy in selected patients
✔ Specialist assessment is important if symptoms are more severe or the diagnosis is uncertain
Book an Oral Allergy Syndrome Assessment
Arrange a specialist consultation for pollen food syndrome, cross-reactive food allergy, hay fever and component-resolved allergy testing.