Oral Allergy Syndrome (OAS), also known as pollen-food allergy syndrome, is a type of food allergy that occurs in people who are allergic to certain pollen proteins and experience allergic reactions when eating raw fruits, vegetables, nuts, or seeds. It’s caused by cross-reactivity between pollen allergens and proteins found in various plant foods.
Underlying Mechanism
Oral allergy syndrome is an IgE-mediated allergic reaction. Here’s how it works:
- Sensitization to Pollen: The immune system develops antibodies (IgE) to certain proteins found in pollens like birch, ragweed, or grasses.
- Cross-Reactivity: Some raw fruits and vegetables contain proteins that are structurally similar to those pollen proteins.
- Immune Response: When a sensitized person eats a cross-reactive food, the immune system mistakenly identifies the food protein as a threat and triggers a localized allergic reaction in the mouth and throat.
Common Pollen-Food Cross-Reactions
| Pollen Allergy | Common Trigger Foods (Raw) |
| Birch | Apple, pear, cherry, peach, carrot, celery, hazelnut |
| Ragweed | Melon (especially cantaloupe), banana, cucumber, zucchini |
| Grass | Tomato, potato, orange, melon |
Symptoms
Symptoms are typically mild and localized to the mouth, lips, tongue, and throat, appearing within minutes of eating the offending food:
- Itching or tingling of the lips, mouth, or throat
- Mild swelling of lips, tongue, or throat
- Scratchy throat
- Redness or irritation inside the mouth
- Occasionally, ear itching
Symptoms usually resolve within 30 minutes and are rarely life-threatening.
Diagnosis
Diagnosis often involves:
- Medical history: Especially history of seasonal allergies and symptom timing related to specific foods
- Skin prick testing: For pollen and food allergens
- Blood tests: Measuring specific IgE levels to pollen and food proteins
- Oral food challenge: Supervised test to confirm reactivity
Prevention and Management
- Avoid raw trigger foods: Cooking denatures the allergenic proteins, so cooked versions are often safe.
- Peeling fruits/vegetables: Many of the proteins are in the skin.
- Avoid during high pollen seasons: Sensitivity can be worse during peak allergy times.
- Antihistamines: Can reduce symptoms if taken before eating known trigger foods.
- Allergen immunotherapy (allergy shots): May reduce both pollen and food symptoms in some patients.
Rare Complications
- Though OAS is usually mild, systemic reactions (e.g., hives, wheezing, or anaphylaxis) can occasionally occur, especially if:
- The person has a history of severe food allergies
- They ingest large quantities of the offending food
- They consume it on an empty stomach or during exercise
Key Takeaways
- OAS is a cross-reaction between pollen and plant food proteins
- It mostly causes mild, oral symptoms
- It’s common in people with seasonal allergic rhinitis
- Cooking or peeling foods can often prevent symptoms
- It’s usually not dangerous, but awareness and management are important
Oral Allergy – Immune Response
