If your child complains that their mouth tingles or itches when they eat certain raw fruits, vegetables or nuts — but has no other symptoms — they may have oral allergy syndrome (OAS), also known as pollen-food allergy syndrome (PFAS). This is a very common condition in children and teenagers with hay fever, and it is important to understand because it is often confused with a true food allergy.

What Is Oral Allergy Syndrome?

Oral allergy syndrome is caused by cross-reactivity between pollen proteins and similar proteins found in certain raw foods. The immune system, already sensitised to pollen, mistakes the food protein for pollen and triggers a localised allergic reaction in the mouth and throat.

The key word is localised. In oral allergy syndrome, symptoms are confined to the mouth, lips, tongue and throat. The food proteins responsible are fragile and are broken down by stomach acid before they can be absorbed into the bloodstream — which is why OAS does not usually cause systemic reactions (hives, vomiting, anaphylaxis).

Symptoms of Oral Allergy Syndrome

Symptoms typically begin within seconds to a few minutes of eating the raw food and include:

  • Tingling, itching or burning sensation in the lips, mouth, tongue or throat
  • Mild swelling of the lips or tongue
  • Itchy ears
  • Scratchy throat

Symptoms usually resolve within a few minutes of stopping eating and spitting out the food. They are typically mild and self-limiting. However, if your child develops symptoms beyond the mouth — such as hives, vomiting, difficulty breathing or throat tightening — this is not OAS and requires urgent medical assessment.

Which Pollens and Foods Are Involved?

The most common pollen-food associations in Northern Ireland are:

  • Birch pollen (spring) → apple, pear, cherry, peach, plum, apricot, nectarine, almond, hazelnut, carrot, celery, parsley, kiwi, soya
  • Grass pollen (summer) → tomato, potato, peach, celery, melon, orange, kiwi, peanut (mild reactions only)
  • Mugwort weed pollen (late summer) → celery, carrot, parsley, coriander, fennel, aniseed, mustard, sunflower seeds

Birch pollen is the most common cause of OAS in Northern Ireland. Children with birch pollen allergy who eat raw apple are a classic example — the apple protein Mal d 1 is structurally similar to the birch pollen protein Bet v 1.

Why Does Cooking the Food Help?

The proteins responsible for OAS are heat-labile — they are destroyed by cooking. This is why children with OAS can usually eat cooked versions of the same foods without any symptoms. For example, a child who reacts to raw apple can usually eat cooked apple (apple sauce, apple pie) without problems. Similarly, roasted hazelnuts are usually tolerated by children with birch-pollen-related hazelnut OAS.

This is an important distinction from true food allergy, where cooking does not reliably prevent reactions.

Is Oral Allergy Syndrome the Same as Food Allergy?

No. OAS is a form of sensitisation driven by pollen allergy, not a primary food allergy. The distinction matters because:

  • OAS does not usually require strict avoidance of the food — many children can eat small amounts or cooked versions without symptoms
  • OAS does not usually require an adrenaline auto-injector
  • OAS is managed primarily by treating the underlying pollen allergy (antihistamines, nasal sprays, and potentially immunotherapy)
  • OAS does not usually worsen over time

However, a small number of children with OAS — particularly those with grass pollen allergy and reactions to peanut — can develop more severe systemic reactions. This is why specialist assessment is important if you are unsure whether your child has OAS or a true food allergy.

When Should I Seek Specialist Assessment?

Seek specialist assessment at Belfast Children's Allergy Clinic if:

  • Your child has symptoms beyond the mouth (hives, vomiting, breathing difficulties)
  • You are unsure whether your child has OAS or a true food allergy
  • Symptoms are severe or distressing
  • Your child has reactions to peanut (even mild ones) — peanut reactions should always be assessed by a specialist
  • Your child's hay fever is poorly controlled

Book an Appointment

Call 028 9066 7878 or book online at kph.fyi/Book-MAnandarajan. No GP referral is required.