Soy allergy is a reaction to foods, ingredients and products derived from soybeans. It can provoke a wide range of symptoms, which range from nasal congestion to potentially more serious manifestations such as bronchospasm (sudden tightening of the airways) and anaphylaxis (a dangerous allergic reaction involving two or more body systems). 

Soybeans are legumes (pods or seeds used as food) that can be found in many foods and food products, including vegetable oils, soy sauces and tofu. Soy is an allergen for some people. Because soy is present in so many foods, those who are allergic to it must be very careful to become familiar with soy-based products and ingredients. Avoidance is the only technique certain to prevent symptoms.  

Soy allergy is more common in infants than any other group. It often appears in the first three months of life, and disappears by the time a child is 2. Soy allergy symptoms are rare in adults.

Soy milk was once considered a good alternative for infants who could not drink regular milk or were at increased risk of food allergies. However, as more and more infants switched to soy milk formulas, it became clear that soy, too, was a potential food allergen (though there is no cross-reactivity between cow's milk and soy – each triggers an allergic reaction independently). For this reason, soy formulas are no longer considered a safer type of formula for at-risk infants.

Laboratory research has had some success with the creation of allergen-free varieties of soybeans. While they have not yet been adopted by the marketplace, allergen-free soybeans could one day begin to replace the allergy-causing lines currently being grown.