TIL If you're allergic to birch, you're probably also allergic to raw apples, cherries, pears, and plums! It's called "Oral Allergy Syndrome," but it can often present GI symptoms.

Text directly quoted from the link.

Occasionally people with Oral Allergy Syndrome also develop symptoms of abdominal pain and vomiting or diarrhea after eating the foods.

People who have high levels of allergic antibodies to the common Birch Pollen allergens usually develop symptoms on eating one or more of the following raw fruits:

• apple

• cherry

• pear

• plum

Less common foods that cause reactions in those who have birch pollen allergy are:

• hazelnut

• celery

• carrot

• soybean

• peanut

• kiwi

• banana

• pineapple

• stone fruits like peach and apricot

• potato (especially cutting up raw potatoes when a person with oral allergy syndrome may develop itchy hands. Wearing gloves usually helps the problem)

• tomato (especially cutting up raw tomato when a patient may develop itchy hands)