Oral allergy syndrome (OAS) occurs when your body mistakes proteins in certain raw foods for the same allergenic proteins in pollen, confusing your immune system and making existing allergy symptoms worse.
A study done by a Japanese found that 10% of patients with birch pollen allergies exhibited sensitivity to soy milk.
Even though soy milk is processed, and wasn’t thought to be able to evoke an OAS response, researchers speculate the symptoms might be due to the fact that soy milk’s protein are not broken down that much during processing, leaving these allergy-inducing compounds apparent in the milk.