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Pediatric Oral Allergy Syndrome (OAS)

Oral allergy syndrome (OAS), also called pollen-food allergy syndrome, is a food allergy that only impacts the lips, mouth and throat. It occurs in children who are allergic to birch, grass, mugwort or ragweed pollens.

What is Pediatric Oral Allergy Syndrome (OAS)?

OAS is a type of food allergy where children experience a reaction only in their lips, mouth and throat. It occurs in children who are allergic to birch, grass, mugwort or ragweed pollens, and is more likely to occur in children who also have asthma.

Adults tend to be affected more than children, but adolescents (age 10-19 years old*) can show symptoms. People can develop the allergy at any point in their lives, including after years of eating the same food and not having a reaction.

What are the signs and symptoms of Pediatric Oral Allergy Syndrome (OAS)?

OAS symptoms normally begin in adolescence and most often develop in the adult years. Symptoms include:

  • Itchy ears, mouth or throat
  • Swelling of the face (lips, mouth throat or tongue)

Anaphylactic shock symptoms

Anaphylactic shock (also called anaphylaxis) is a severe allergic reaction that comes on rapidly and must be treated immediately. Symptoms include:

*Age of adolescents as defined by the World Health Organization.

What are the causes of Pediatric Oral Allergy Syndrome (OAS)?

OAS occurs when a child eats a raw fruit, vegetable or tree nut, and it causes a cross-reaction with a birch, grass, mugwort or ragweed pollen allergy. Often, a child with OAS can eat the same food when it’s cooked and it will not trigger a reaction.  


Triggers vary between children, as do allergies and the severity of the reaction to each trigger. When a child is allergic to birch, grass, mugwort or ragweed pollen, they are more likely to have a cross-reaction when they eat the foods listed below.

Birch Pollen

  • Apples, kiwis and pears
  • Almonds and hazelnuts
  • Carrots and celery
  • Cherries, peaches and plums

Grass Pollen

  • Celery
  • Melons and peaches
  • Oranges
  • Tomatoes

Mugwort pollen

  • Cauliflower, broccoli and cabbage
  • Onion and bell peppers
  • Spices like black pepper, garlic, parsley and coriander

Ragweed Pollen

  • Bananas
  • Cucumbers
  • Melons
  • Sunflower seeds 
  • Zucchini