Why can I eat cooked apple but a raw apple makes my mouth itch?

The proteins that trigger oral allergy syndrome are fragile and destroyed by heat, so cooking, baking or canning usually makes the same food safe. Raw forms keep the intact protein that cross-reacts with your pollen allergy.

Is oral allergy syndrome dangerous?

It is usually mild and limited to the mouth, settling within about half an hour. However, a small minority of people have more serious whole-body reactions, so learn the warning signs and get urgent care if your throat tightens or you have trouble breathing.

Do I have hay fever if I have OAS?

Almost always — OAS occurs in people already sensitised to pollen, and it is really a cross-reaction between pollen and similar food proteins. Many people notice mouth symptoms are worse during their pollen-allergy season.

Do the food lists apply in Singapore?

Not necessarily. The classic pollen-food lists come from regions with heavy seasonal pollen like birch or ragweed, and Singapore’s pollen exposure is different, so treat those lists as examples only. What matters is which specific raw foods trigger your own symptoms.

Do I need to carry an adrenaline pen?

Most people with typical mouth-only OAS do not. A pen is prescribed only if you have had a reaction that spread beyond the mouth, or an allergist judges you at higher risk — for example with nut triggers or reactions to cooked foods.

Oral Allergy Syndrome in Singapore: Itchy Mouth Foods

Written & reviewed by the BestDoctors.sg editorial team · Last updated 24 Aug 2026 · General information, not medical advice

Oral allergy syndrome (OAS), more precisely called pollen-food allergy syndrome, is an allergic reaction — usually mild and limited to the mouth — that occurs when people already sensitised to pollen eat certain raw fruits, vegetables or nuts. It happens because some raw plant-food proteins closely resemble pollen proteins, so the immune system’s antibodies “mistake” the food for pollen and react in the mouth. It is essentially a downstream consequence of hay-fever-type allergic rhinitis.

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In a medical emergency, or for severe or sudden symptoms such as breathing difficulty, chest pain, fainting or stroke signs, call 995 immediately.

OAS is usually mild, but a small minority of people progress beyond the mouth — any throat tightness, trouble breathing or swallowing, widespread hives or faintness means calling 995.

Why cooking usually makes it safe

The proteins responsible for OAS are fragile: they are broken down by heat and by stomach acid. This is why cooked, baked, canned or heavily processed forms of the same food are usually tolerated, and why symptoms tend to stay in the mouth — the protein is destroyed before it is absorbed. For some fruits, peeling reduces (but does not remove) the reaction because the protein concentrates near the skin.

Triggers — and a Singapore caveat

The classic pollen-food associations — such as birch pollen with apple, pear, peach, cherry, kiwi, carrot and hazelnut, or ragweed with banana, melon and cucumber — come mainly from temperate regions with heavy seasonal pollen. Singapore’s pollen exposure profile is different, so these lists should be treated as illustrative examples rather than a Singapore-specific list. What matters far more is which specific raw foods trigger your symptoms. Reactions are typically to the raw food; the same food cooked is usually fine.

Symptoms

Symptoms come on quickly — usually within about 5 to 10 minutes of eating — and typically settle within around half an hour once the food is removed or swallowed. They are usually confined to areas that touch the food: itchy or tingling lips, mouth, tongue and palate, a scratchy throat, mild lip or mouth swelling, and sometimes itchy ears. Symptoms may be worse during a person’s pollen-allergy season and in those with more severe hay fever.

Red flags

Although OAS is usually mild, a small minority of reactions spread beyond the mouth. Seek urgent or emergency care (call 995) for throat tightness or difficulty swallowing or breathing, a voice change, widespread hives, swelling of the tongue or throat, wheeze, vomiting, dizziness, faintness or collapse — these suggest a systemic reaction or anaphylaxis rather than simple OAS. Higher-risk clues that warrant allergist review include reactions to nuts, reactions to cooked as well as raw food, or any past reaction that spread beyond the mouth — these can indicate a true, more dangerous food allergy.

Diagnosis and treatment

OAS is assessed by an allergist or, initially, a GP, and diagnosis is mainly clinical: a careful history of which raw foods cause symptoms, how quickly they start, whether cooked forms are tolerated, and whether the person has pollen allergy. Supportive testing, when needed, includes skin-prick testing (sometimes with the fresh raw food) and blood tests for specific IgE, including component testing that helps gauge whether a reaction is likely to stay mild or could be systemic. Management centres on avoiding the raw trigger foods that affect you — there is no need to avoid foods that cause no symptoms — and on cooking, baking or otherwise heating the food, which usually makes it tolerable. Oral antihistamines relieve mild mouth symptoms; often no treatment is needed once the food is removed. An adrenaline auto-injector is prescribed only for those who have had, or are judged at risk of, systemic reactions, not for typical mouth-only OAS.

Practical ways to manage it

Most people manage oral allergy syndrome well with a few adjustments rather than broad avoidance. Because heat breaks down the responsible proteins, the same fruit or vegetable is usually fine cooked, baked, canned, stewed or microwaved, so you rarely need to give a food up entirely — you simply change how you eat it. Peeling certain fruits, choosing tinned or well-cooked versions, and being a little more careful during your pollen-allergy season can all reduce symptoms. Keep a simple note of which raw foods cause the tingling and how strong the reaction is, as this helps you and your doctor judge whether it is staying mild and mouth-limited or showing any sign of spreading. If your reactions are typical and mild, an antihistamine on hand is usually all that is needed; if there is any history of a reaction beyond the mouth, follow your allergist’s advice on carrying emergency medication.

When to see a doctor

See a GP or allergist to confirm the diagnosis if you regularly get an itchy or tingly mouth after raw fruit, vegetables or nuts — especially to be sure it is OAS and not a more serious food allergy. Seek specialist review sooner if reactions involve nuts, occur with cooked foods, are getting worse or more widespread, or if you have significant asthma. Call 995 for any throat tightness, breathing difficulty, widespread swelling or faintness.

Related allergy & immunology topics

Sources

AAAAI — Oral Allergy Syndrome (OAS) Defined: aaaai.org
ACAAI — Pollen Food Allergy Syndrome: acaai.org
DermNet — Pollen-food allergy syndrome: dermnetnz.org
Cleveland Clinic — Oral Allergy Syndrome: clevelandclinic.org

General information only. This guide is general information about an allergy or immunology condition and is not a diagnosis or personalised medical advice. See a doctor — a GP or an allergist/immunologist — for assessment; allergy-test results show sensitisation and must be interpreted by a doctor alongside your history. Call 995 for anaphylaxis — sudden swelling of the lips, tongue or throat, difficulty breathing, a widespread rash with faintness, or collapse — and use an adrenaline auto-injector first if you have one. Swelling of the tongue or throat, or food that is completely stuck so you cannot swallow your own saliva, needs emergency care.