Oral Allergy Syndrome (OAS / PFAS)
View All Tests⚠️ When OAS may be more than "just an itchy mouth"
Classic OAS is mild and short-lived. However, a small minority of people develop symptoms beyond the mouth — widespread hives, facial swelling, wheeze, vomiting or feeling faint — and rarely anaphylaxis. This is particularly relevant if you are sensitised to lipid transfer proteins (LTPs), which are heat-stable and can persist through cooking.
If you have ever had symptoms beyond your mouth after eating fruit, nuts or vegetables — or if a reaction has needed an antihistamine, adrenaline or A&E — please see your GP for assessment and discussion of allergy specialist referral before relying on testing alone. If you have been prescribed an adrenaline auto-injector (EpiPen, Jext or Emerade), carry it at all times.
What Is Oral Allergy Syndrome?
Oral allergy syndrome (OAS) — also called pollen-food allergy syndrome (PFAS) or sometimes pollen-food syndrome — is the most common type of food allergy in adults. It develops in people who are sensitised to certain airborne pollens and then react to raw fruits, vegetables, nuts or spices that contain proteins structurally similar to those pollens.
The cross-reactivity is mediated by panallergens — protein families conserved across the plant kingdom. The most important ones are the PR-10 family (Bet v 1-like), profilins, polcalcins, and lipid transfer proteins (LTPs). The pollen always comes first: people are sensitised through breathing in pollen during the season and only later notice symptoms when they eat the related food.
OAS is a clinical diagnosis made by a doctor — usually a GP or allergy specialist — based on the pattern of symptoms, the foods involved and serological evidence of pollen sensitisation. Component-resolved IgE blood testing has a supportive role: it can clarify which panallergens you are sensitised to, which often correlates with the expected pattern of food reactions.
Typical Symptoms
Symptoms usually begin within 5 to 15 minutes of food contact with the mucosa, are localised to the mouth and throat, and resolve within around 30 minutes once the food is removed.
- · Itching of the lips, tongue, palate or throat
- · Tingling or burning sensation on the mucosa
- · Mild lip swelling
- · Itchy ears (sometimes described as "tickling deep inside")
- · Scratchy throat
- · Occasional mild sneezing or runny nose during the meal
Symptoms often worsen during the relevant pollen season and improve outside it. They typically come on with raw, fresh or ripe versions of the food — cooked, baked, canned or processed versions are usually tolerated, because the responsible proteins (PR-10) are destroyed by heat.
The Main Pollen-Food Cross-Reactivity Patterns
Three pollen-food patterns are particularly common in the UK and Europe. People can be sensitised to more than one, especially if they have several seasonal allergies.
| Pollen | Key panallergen | Commonly cross-reactive foods |
|---|---|---|
| Birch (Bet v 1) | PR-10 | Apple, pear, peach, cherry, plum, apricot, kiwi, hazelnut, almond, walnut, carrot, celery, soybean (Gly m 4), peanut (Ara h 8) |
| Grass (Phl p 1, Phl p 12) | Profilin / Group 1 | Tomato, melon, watermelon, orange, kiwi, peanut, wheat, potato |
| Mugwort (Art v 1, Art v 3) | Defensin-like / LTP | Celery, carrot, parsnip, fennel, parsley, coriander, spices (cumin, paprika, pepper), peach, mustard, sunflower seeds |
| Ragweed (Amb a 1) | Profilin / various | Melon, watermelon, banana, cucumber, courgette |
This table shows commonly reported patterns — not personal predictions. Many sensitised individuals only react to a handful of foods in their group, and some tolerate them all. Component testing helps narrow this down.
The Science: PR-10, Profilins, Polcalcins & LTP
Modern component-resolved diagnostics let us see which protein your immune system is recognising — not just whether you are sensitised to birch or grass. That distinction matters because each panallergen family behaves differently in clinical reactions.
PR-10 (Pathogenesis-Related Protein 10) — e.g. Bet v 1
The classic driver of birch-related OAS. Heat-labile (destroyed by cooking), acid-labile (broken down by stomach acid). Reactions are usually mild, local and limited to the mouth and throat.
Profilins — e.g. Bet v 2, Phl p 12
A second panallergen family found across most plants. Profilin sensitisation often shows on broad allergen tests but, on its own, is usually of limited clinical relevance. Helpful for explaining widespread "positive" results without obvious clinical reactions.
Polcalcins — e.g. Bet v 4, Phl p 7
Calcium-binding proteins shared across pollens. Polcalcin sensitisation typically indicates true pollen-driven allergy and broad pollen cross- reactivity, but is rarely a direct food trigger.
Lipid Transfer Proteins (LTPs) — e.g. Pru p 3, Art v 3
The most clinically important panallergens to identify, because they are heat- and acid-stable. LTP sensitisation can cause more severe, systemic reactions and is more common in Mediterranean populations but also seen in the UK. Pru p 3 (peach LTP) is the prototype.
How Testing Works
Choose Your Test
Select from our range of allergy blood tests and book a convenient time at our South Kensington clinic. No GP referral needed.
Nurse Blood Draw
A qualified nurse takes a small blood sample at our clinic. The appointment is quick and straightforward.
Get Your Results
Results are sent directly to you, typically within a few working days. Share them with your GP or specialist to guide your next steps.
Component-Resolved Testing for OAS
For someone whose symptoms suggest OAS, component-resolved blood testing can clarify the panallergen pattern driving the reactions. The starting point is usually a birch components test (covers Bet v 1, Bet v 2, Bet v 4) combined with the UK aero-allergen profile. For a broader picture across around 300 allergens — including profilins, polcalcins and LTPs — the multiplex ALEX² test is the most comprehensive single panel. Results are released to you to share with your GP or allergy specialist.
View the Birch Components Test →Often paired with:
Tests Relevant to OAS
Our Role in Investigating OAS
AllergyClinic.co.uk is a CQC-registered, nurse-led diagnostic service. All blood samples are taken by registered nurses experienced in allergy and component-resolved testing pathways, processed by an accredited laboratory, and returned to you as a clearly formatted report. We do not diagnose OAS, interpret your results into a clinical decision, or recommend dietary restrictions — those steps sit with your GP, allergy specialist or registered dietitian.
A practical pathway for someone with suspected OAS in the UK is: GP review → component-resolved IgE testing (birch components, profilins, polcalcins or a multiplex panel) → allergy specialist referral if symptoms are systemic, severe or unclear → individualised advice from a dietitian. Private testing through our clinic can be a useful intermediate step to bring well-organised results to your GP appointment.
Why Choose a Diagnostic-Only Clinic?
Unlike clinics that provide both testing and treatment, our nurse-led service focuses solely on accurate diagnostic testing. Because we don't offer treatments or prescriptions, there is no commercial incentive to recommend unnecessary tests — just honest, impartial results you can trust.
Nurse-Led & Impartial
Our qualified nurses collect your sample — we don't prescribe, treat, or have any reason to upsell.
Results You Own
Your results are sent directly to you. Take them to your GP or a specialist to discuss what's best for your situation.
You Stay in Control
Understand your allergy profile, then decide with your healthcare professional what steps to take next.
Related Conditions
Related Reading
- → Oral Allergy Syndrome: Why Fresh Fruit Makes Your Mouth Itch
- → Oral Allergy Syndrome: The Pollen-Food Connection (London)
- → Oral Allergy Syndrome vs Nut Allergy: How to Tell the Difference
- → Apple Allergy vs Birch Pollen: Understanding Cross-Reactivity
- → Can You Be Allergic to Avocados? OAS Link
- → Banana Allergy & Latex Cross-Reactivity
- → Itchy Throat After Fruit: Pesticides vs Protein Allergy
- → Pork-Cat Syndrome: Cross-Reactivity Explained
Frequently Asked Questions
What are the symptoms of oral allergy syndrome?
Oral allergy syndrome (OAS) typically causes itching or tingling of the lips, tongue, mouth, palate and throat within 5 to 15 minutes of eating certain fresh fruits, vegetables or nuts. Some people notice mild swelling of the lips, a scratchy throat or itchy ears. Symptoms usually settle within 30 minutes once the food is no longer in contact with the mucosa. The reaction is local and, in most cases, mild — but a small minority of people can experience more systemic symptoms or, very rarely, anaphylaxis.
Why does pollen allergy make me react to certain fruits and vegetables?
Some plant proteins look very similar to one another — even across distant species. When your immune system has been sensitised to a pollen protein (for example, the major birch allergen Bet v 1), it can also recognise structurally homologous proteins found in certain raw fruits, nuts and vegetables. This is called pollen-food allergy syndrome (PFAS). The most common UK pattern is birch pollen with apple, hazelnut, peach and stone fruits.
Why are cooked or canned versions of the food usually fine?
The cross-reactive proteins involved in classic OAS — particularly PR-10 proteins like Bet v 1 — are heat-labile, meaning they are destroyed by cooking, baking, microwaving or canning. That is why someone with birch-apple OAS may itch after a fresh apple but tolerate apple pie. There is one important exception: lipid transfer proteins (LTPs), found especially in peach and other Mediterranean fruits, are heat-stable and can persist through cooking.
How does the birch components blood test help?
The birch components test measures specific IgE to individual birch allergen molecules rather than to the whole birch extract. It distinguishes sensitisation to the major birch protein Bet v 1 (linked to typical mild OAS) from sensitisation to minor cross-reactive panallergens like profilins (Bet v 2) or polcalcins (Bet v 4). The pattern your immune system shows often helps an allergy specialist predict the likely clinical relevance and pollen-food cross-reactivity.
Is oral allergy syndrome dangerous?
In the vast majority of people, OAS is mild and self-limiting. However, around 1 to 3% of patients with classic OAS may progress to more systemic symptoms, and rare individuals — particularly those with LTP sensitisation — can experience severe reactions including anaphylaxis. If you have ever had symptoms beyond the mouth and throat (such as widespread hives, wheeze, vomiting or feeling faint), please see your GP for assessment and discussion of an allergy specialist referral.
Do I need to avoid all raw fruits and vegetables?
No. Avoidance advice in OAS is highly individual and should not be applied as a blanket restriction. Many people only react to a small subset of foods within their cross-reactive group. Component testing helps narrow this down. Avoidance decisions — particularly in children, pregnant women or anyone where wider dietary restriction is being considered — should be guided by an allergy specialist or registered dietitian.
Related reading
Can You Be Allergic to Avocados? The Oral Allergy Syndrome Link
Yes, you can be allergic to avocados. Avocado allergies commonly develop through oral allergy syndrome (OAS), where proteins in avocados cross-react with tree pollens like birch. T
Read article →
Oral Allergy Syndrome vs. Nut Allergy: How to Tell the Difference
Oral allergy syndrome (OAS) is a cross-reactive allergic response that typically causes mild mouth and throat symptoms when eating certain raw fruits and nuts, whilst true nut alle
Read article →
Oral Allergy Syndrome: Why Fresh Fruit Makes Your Mouth Itch
Learn why raw fruit makes your mouth itch. Understand oral allergy syndrome, pollen food syndrome, birch apple allergy, cross-reactivity, and when IgE blood testing may help. Evidence-based UK guide.
Read article →Clarify Pollen-Food Cross-Reactivity
Component-resolved blood testing distinguishes mild birch-driven OAS from higher-risk LTP sensitisation. Sample collected by a nurse at our South Kensington clinic — results released to you to share with your GP or allergy specialist.
View the Birch Components Test →