Allergist and Immunologist Questions Allergies

Why am I allergic to just soy milk and no other soy product?

I cannot tolerate soymilk. I do not have a life-threatening allergy, but when I've had it in the past, everything from my lips down my throat becomes swollen and itchy. However, I can eat soy beans, tofu, and other soy products just fine. What is it about soy milk?

4 Answers

Very good question. Many of the other products contain soy lecithin or soy oil which are devoid of actual soy protein which is the molecule that the human immune system develops an allergy to. While soy beans and tofu do have concentrated soy protein cooking those products (the heat during cooking) alters the structure of the protein and is some patients (like you) that prevents the immune system from recognizing the trigger thus not triggering an immune response. So, as long as they do not bother you keep eating those foods - I suggest avoidance of soy milk as you have alternatives and there is no need to unnecessarily stimulate your immune system. 
Hope that helps. 

Sincerely, 

Monika Korff, MD
That's a tough question to answer. Since you tolerate soybeans you may not be allergic to soy protein. Most people allergic to soy protein can tolerate some soy products. Soy sauce is made by fermenting soy beans and this appears to render the allergens inactive for most soy-allergic individuals. Soy lecithin is a fat and contains no soy allergen (unless as a contaminant) so that too is typically tolerated by soy-allergic persons. Soy "milk" is not a true milk and often contains other ingredients to make the beverage more milk-like in consistency, smoothness, pour-ability and taste. Some of these ingredients may be vegetable gums or natural flavors. You might be allergic to these extra ingredients rather than to soy. You should be able to resolve this problem with the assistance of a board-certified allergist. Alternatively you could try other brands of soy milk to see if this problem occurs with all or most of them or with just one brand.


Steve Machtinger, MD FAAAAI
My suspicion is because soy "milk" is not processed (i.e. it is "raw"). Without knowing what brand of soy milk you drink and how they process the "milk", this is just a guess.
With a soy allergy, your immune system identifies certain soy proteins as harmful, triggering the production of immunoglobulin E (IgE) antibodies to the soy protein (allergen). The next time you come in contact with soy, these IgE antibodies recognize it and signal your immune system to release histamine and other chemicals into your bloodstream.