Soy allergy

What it is

Soy allergy is an immune reaction to proteins in soybeans. In people with the allergy, soy proteins bind to IgE antibodies, which sets off the reaction.⁶ Soybeans are legumes, the same plant family as beans, peas, lentils and peanuts.⁶ Soy is a common ingredient in infant formulas and in many processed foods.⁵

Soy is one of the most common food allergens in young children. Reactions usually first appear in infants and children under 3, and many children outgrow the allergy during childhood.⁵ Some people stay allergic for life.⁶

Symptoms it causes

Soy allergy symptoms follow eating soy, and they can involve the skin, the gut, breathing and circulation. ACAAI lists hives and swelling of the tongue or lips; vomiting, stomach cramps, indigestion and diarrhea; wheezing, shortness of breath, a repeated cough, a tight throat or a hoarse voice; and a weak pulse, pale or blue skin, dizziness or confusion.⁵ Food allergy symptoms can begin within a few minutes to a few hours after eating.²

Most soy reactions are mild, but they are hard to predict.⁶ A severe reaction that affects the whole body, called anaphylaxis, is rare with soy but can happen. It can make breathing hard and cause a sudden drop in blood pressure, sending the body into shock.⁵

Reading food labels

Soy is a major food allergen under US law, so packaged foods must name it in plain words. The Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) made soybeans one of eight major food allergens.³ The FASTER Act added sesame in 2021, which brought the list to nine.¹ FDA enforces these rules for the foods it regulates; poultry, most meats, certain egg products and most alcoholic drinks fall under other agencies.²

The label has to name soy at least once, in one of two ways: in parentheses after an ingredient, as in “lecithin (soy),” or in a “Contains” statement right after or next to the ingredient list.¹ FDA accepts “soy,” “soybean” or “soya” as the name of the food source.⁴

Oils follow their own rule. Highly refined soybean oil is exempt from allergen labeling, but the ingredient list still has to call it soybean oil. Soy oil that is not highly refined must be declared as soy.⁴ FARE notes that cold-pressed, expelled and extruded soy oils are not highly refined.⁶

Statements such as “may contain soy” are not required by law. FDA says they must be truthful and not misleading, and they cannot stand in for good manufacturing practices.¹

Soy can show up where people may not expect it. ACAAI and FARE list canned broths and soups, canned tuna, processed meats and hot dogs, energy bars, baked goods, cereals and crackers, low-fat peanut butter, vegetarian meat alternatives and many Asian dishes.⁵⁶ Ingredient names that mean soy include edamame, miso, natto, okara, shoyu, tamari, tempeh, tofu and textured vegetable protein.⁶ Outside food, FARE lists soaps, moisturizers, other personal care products and pet food.⁶