OAS is caused by allergens in fruits, vegetables, tree nuts, and peanuts that are homologous to pollen allergens.
Cross-reactivity in Pollen-Food Allergy Syndrome (PFAS) or Oral Allergy Syndrome (OAS) (click to enlarge the image).
Cross-reactivity list in oral allergy syndrome (pollen-food allergy syndrome): http://bit.ly/dFuk1
Flavored Coffee May Trigger Seasonal Allergies - due to oral allergy syndrome. Fox News, 2011.
Which allergen cross-reacts with Bet v1 (birch)?
(A) Ara h1 (peanut)
(B) Mal d 1 (apple)
(C) Ara h3 (peanut)
(D) Bos d (milk)
(E) Gal d (egg)
(F) Hev b2 (latex)
Answer: B, apple. Pollen sensitizations linked to food allergies was first reported with birch pollen and apples 50 years ago.
Profilin may be a pan-allergen among plants that crossreacts between pollen, fruits, vegetables and latex http://goo.gl/ZUPRQ
Cross Reactions Among Foods (PDF).