Causes

An immune system reaction causes food allergies. 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.

Histamine and other body chemicals cause a range of allergic signs and symptoms. Histamine is partly responsible for most allergic responses, including a runny nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, difficulty breathing, and anaphylactic shock.

Food protein-induced enterocolitis syndrome (FPIES)

A food allergen can also cause what's sometimes called a delayed food allergy. Although any food can be a trigger, soy is one of the more common in children. The reaction, commonly vomiting and diarrhea, usually occurs within hours after eating the trigger, rather than minutes.

Unlike some food allergies, FPIES usually resolves over time. As with typical soy allergies, preventing a reaction involves avoiding foods with soy.