Cross-Reactivity & Oral Allergy Syndrome (OAS)
What is Oral Allergy Syndrome?
Oral Allergy Syndrome (OAS), also called pollen-food syndrome, happens when your immune system mistakes proteins in certain raw fruits, vegetables, and nuts for pollen proteins. If you’re allergic to specific pollens, eating certain foods may cause itching or tingling in your mouth, lips, throat, and ears.
This occurs because the proteins in these foods are structurally similar to pollen allergens — your immune system can’t tell the difference. About 50-75% of people with birch pollen allergies experience OAS, and it’s common with other pollen sensitivities too.
Common Symptoms
OAS symptoms usually appear within minutes of eating the trigger food and mostly affect the mouth and throat:
- Itching or tingling of lips, mouth, tongue, and throat
- Mild swelling of lips, tongue, or throat
- Scratchy or irritated throat
- Itchy ears
Symptoms are usually mild and go away quickly once you stop eating the food. Severe reactions are rare but can occur, particularly with nuts.
Pollen-Food Cross-Reactivity Chart
Birch Pollen
Birch is the most common cause of OAS. If you’re allergic to birch, you may react to:
| Food Category | Cross-Reactive Foods |
|---|---|
| Fruits | Apple, pear, cherry, peach, plum, apricot, nectarine, kiwi |
| Vegetables | Carrot, celery, parsley, fennel, coriander |
| Nuts | Hazelnut, almond, walnut |
| Legumes | Soybean, peanut |
| Spices | Anise, cumin, caraway |
Mugwort Pollen (Celery-Mugwort-Spice Syndrome)
Mugwort cross-reactivity often involves a wider range of foods and spices:
| Food Category | Cross-Reactive Foods |
|---|---|
| Vegetables | Celery, carrot, parsley, fennel |
| Fruits | Apple, melon, watermelon, mango |
| Spices | Pepper, mustard, coriander, cumin, anise, fennel seed |
| Nuts | Sunflower seeds |
Learn more about Mugwort pollen
Ragweed Pollen
| Food Category | Cross-Reactive Foods |
|---|---|
| Fruits | Banana, melon (cantaloupe, honeydew, watermelon) |
| Vegetables | Cucumber, zucchini |
| Other | Chamomile tea, sunflower seeds |
Learn more about Ragweed pollen
Grass Pollen
| Food Category | Cross-Reactive Foods |
|---|---|
| Fruits | Melon, orange, tomato, watermelon |
| Vegetables | Potato (raw), celery |
| Grains | Wheat (in some cases) |
Alder Pollen
Similar to birch since they’re in the same family:
| Food Category | Cross-Reactive Foods |
|---|---|
| Fruits | Apple, cherry, pear, peach, strawberry |
| Vegetables | Celery, parsley |
| Nuts | Hazelnut, almond |
Managing OAS
Cooking Reduces Reactions
Heat breaks down the proteins that cause OAS. Most people can eat the same foods when cooked, baked, canned, or processed:
- Apple pie instead of raw apple
- Cooked carrots instead of raw
- Roasted hazelnuts instead of raw
- Tomato sauce instead of raw tomato
Peeling May Help
Some trigger proteins concentrate in the skin. Peeling fruits like apples or peaches may reduce or eliminate symptoms for some people.
Seasonal Variation
OAS symptoms often get worse during pollen season. You may tolerate certain foods outside of allergy season but react to them when pollen counts are high.
When to Seek Medical Advice
See an allergist if you experience:
- Symptoms beyond the mouth and throat
- Difficulty breathing or swallowing
- Reactions to cooked versions of foods
- Reactions that seem to worsen over time
- Severe reactions to nuts (peanut, tree nuts)
Related Cross-Reactivity
Latex-Fruit Syndrome
People allergic to latex may react to banana, avocado, kiwi, chestnut, and passion fruit.
Lipid Transfer Protein (LTP) Syndrome
A more severe form of plant food allergy, common in Mediterranean regions. Unlike OAS, LTP allergies cause reactions to cooked foods and can trigger systemic symptoms. Common triggers include peach, apple, grape, and nuts.