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Introduction
This time of year, I see many patients who complain of an itchy mouth with watermelon, bananas, apples, or other fresh produce. They ask: “Why does this happen, and what can I do?”
One of the first things I ask is whether they tolerate bananas in banana bread but not raw bananas. If they say yes, that points me toward oral allergy syndrome (OAS), also called food pollen syndrome.
OAS affects people with hay fever or pollen allergies and can cause mouth or throat itchiness after eating raw fruits, vegetables, or certain nuts. It occurs in up to 50–75% of adults allergic to birch pollen.
Why Does This Happen?
OAS occurs because the immune system is tricked.
- Proteins in some fruits and vegetables resemble those in certain pollens.
- When eaten raw, the immune system mistakes the food for pollen and reacts.
- Cooking or processing (like baking bananas into banana bread) changes the protein structure so it no longer resembles pollen, making it “safe.”
It’s important to note that some people do have true food allergies to these foods, which is why detailed history and proper validated testing are critical.
Common Symptoms of OAS
- Itchiness or swelling of the mouth, face, lips, tongue, and throat
- Rash around the mouth
- Upset stomach
- Symptoms appear immediately or within an hour of eating raw fruits, veggies, certain nuts, or grains
Severe reactions are rare, but not impossible. Occasionally, OAS can cause significant swelling, making swallowing or breathing difficult.
Diagnosis and Testing
Food allergy testing often produces mixed results in OAS and doesn’t always match the history. As with all food allergies, the patient’s history is the most important part of the evaluation.
Testing can help identify those with a true food allergy to a fruit or vegetable that’s not just cross-reactive with pollen.
Managing Oral Allergy Syndrome
The American Academy of Allergy, Asthma, and Immunology (AAAAI) offers these tips:
- Avoid raw trigger foods, especially during allergy season
- Eat the foods baked, cooked, or microwaved
- Peel fruits and vegetables, since proteins often concentrate in the skin
- Allergy shots may help reduce OAS symptoms in some patients
When to See a Doctor
Talk to your physician if:
- OAS causes significant throat discomfort
- Symptoms are getting progressively worse
- Symptoms occur with cooked fruits or vegetables
- Symptoms are triggered by nuts
- You develop systemic symptoms like hives, vomiting, or difficulty breathing
Reference
American Academy of Allergy, Asthma, and Immunology – Oral Allergy Syndrome (OAS)
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