Cross-Reactivity & Oral Allergy Syndrome (OAS)
What is Oral Allergy Syndrome?
Oral Allergy Syndrome (OAS), also known as pollen-food syndrome, is an allergic reaction that occurs when your immune system recognizes similarities between pollen proteins and proteins in certain raw fruits, vegetables, and nuts. If you’re allergic to specific pollens, eating certain foods may cause itching or tingling in your mouth, lips, throat, and ears.
This happens because the proteins in these foods are structurally similar to pollen allergens. Your immune system mistakes the food proteins for pollen and triggers an allergic response. The condition affects 50-75% of people with birch pollen allergies and is common among those with other pollen sensitivities.
Common Symptoms
OAS symptoms typically appear within minutes of eating the trigger food and usually affect the mouth and throat:
- Itching or tingling of the lips, mouth, tongue, and throat
- Mild swelling of the lips, tongue, or throat
- Scratchy or irritated throat
- Itchy ears
Symptoms are usually mild and resolve quickly once you stop eating the food. Severe reactions are rare but can occur in some individuals, particularly with nuts.
Pollen-Food Cross-Reactivity Chart
Birch Pollen
The most common cause of OAS. If you’re allergic to birch pollen, 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 due to the Betulaceae family relationship:
| 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 responsible for OAS. Most people with OAS can eat the same foods when they’re 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 are concentrated in the skin. Peeling fruits like apples or peaches may reduce or eliminate symptoms for some people.
Seasonal Variation
OAS symptoms often worsen 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
Consult 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.