Soy allergy affects approximately 1 percent of people in the United States. Soy, also called soya, is among the top eight most common foods that trigger allergies in children. In many cases soy allergy starts with a reaction to a soy-based infant formula. Although most children outgrow soy allergy by age 3, soy allergy may persist and is becoming more common in adults.
In most cases signs and symptoms of soy allergy are mild. Severe allergic reactions are more common with other food allergens than with soy, but in rare cases, soy allergy can cause a life-threatening allergic reaction (anaphylaxis). Deaths linked to soy allergy have occurred in people who also had both severe peanut allergy and asthma. You can reduce your risk of having an allergic reaction to soy by knowing as much as you can about soy allergy and how to avoid soy-containing products.
For most people, an allergic reaction to soy is uncomfortable but not serious. Rarely, an allergic reaction to soy can be frightening and even life-threatening. Signs and symptoms of a food allergy usually develop within a few minutes to an hour after eating soy-containing food.
Symptoms of a soy allergy can include:
- Tingling in the mouth
- Hives, itching or eczema
- Swelling of the lips, face, tongue and throat, or other parts of the body
- Canker sores
- Wheezing, runny nose or trouble breathing
- Abdominal pain, diarrhea, nausea or vomiting
- Dizziness, lightheadedness or fainting
A severe allergic reaction to soy — called anaphylaxis — is rare. It's more likely to occur in people who have asthma or are also allergic to other foods such as peanuts. Anaphylaxis causes more extreme signs and symptoms including:
- Constriction of airways, including a swollen throat or a lump in your throat, that makes it difficult to breathe
- Shock, with a severe drop in blood pressure
- Rapid pulse
- Dizziness, lightheadedness or loss of consciousness
What causes it?
All food allergies are caused by an immune system malfunction. Your immune system identifies certain soy proteins as harmful, triggering the production of immunoglobulin E (IgE) antibodies to neutralize 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 runny nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing, and even anaphylactic shock.
Researchers have identified at least 16 possible soy protein allergens — but exactly how they cause an allergic reaction is still not clear.