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A soy allergy, like any allergy, is when your immune system identifies soy proteins as harmful. When you come into contact with these proteins, your immune system releases histamines, which then cause your allergic symptoms.
As a high-protein member of the legume family, soy is a common ingredient in infant formulas1 and is an important source of protein worldwide. Many vegetarians and vegans rely on soybeans as a great way to get protein in their diets.
In young children, soy is one of the more common food allergens.1 Typically, allergic reactions first appear in infants and children under 3, and most of them outgrow the allergy by age 10.2
Soy allergy symptoms vary from person to person, but most reactions are stomach or skin related. Reactions can also range from mild to severe, including the life-threatening reaction anaphylaxis.3-5
Common signs and symptoms of a soy allergy can include:
Although soybeans themselves may not be a part of many diets, soy can be a hidden ingredient in many foods—that’s why it is important to read the label or and ask about ingredients before buying or eating certain foods. Ingredients in packaged foods can change at any time—and without warning—so check the ingredients carefully every time.
Soybeans and products made from the bean—like miso or tofu—make up a substantial part of the diet in Asia. This is one reason why Asian cuisines are considered high-risk if you have a confirmed soy allergy diagnosis. There is also the possibility of cross-contact or cross-contamination—when one food comes into contact with another food and their proteins mix—even if you order a soy-free dish.
Soybean oil is also used in some industrial components. It can be found in linoleum and glue in the plywood industry, where it is considered an occupational allergen.
Soy can be found in many processed foods, including:
Cross-reactivity is when the proteins in one food item are similar to the proteins in another and your body's immune system views them as the same. There is a high degree of cross-reactivity between soy and birch trees. Up to 10% of all patients with birch sensitization may also be at risk of reactions to soy, including anaphylaxis.5 So, people who are allergic to birch-related tree pollens are often advised to also avoid eating or drinking large amounts of low-processed soy, like soy milk,6 and particularly during pollen season.
Many people are so used to living with—or being embarrassed by—their symptoms that they never consider asking for help. So, how do you know if your symptoms are caused by a soy allergy, a birch allergy, or something else? If you think you or a loved one has a soy allergy, don’t try to manage the problem on your own. A simple blood test can help identify underlying allergen triggers, if you have an allergy. Regular retesting helps follow tolerance development of soy allergies, since the majority of children do outgrow their soy allergy.