What is it?
Soy, a product of soybeans, is one of the common foods that can cause 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. In rare cases, soy allergy can cause a life-threatening allergic reaction (anaphylaxis). 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.
If you or your child has a reaction to soy, tell your doctor about it, no matter how mild the reaction may have been. Tests can help confirm a soy allergy, so you can take steps to avoid future and potentially worse reactions.
For most people, soy allergy 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.
Soy allergy symptoms can include:
- Tingling in the mouth
- Hives, itching or eczema
- Swelling of the lips, face, tongue and throat, or other parts of the body
- 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
Soy allergy in infants often begins with the introduction of a soy-based formula. In many cases, soy allergy develops when a child is switched to a soy-based formula after an allergic reaction to a milk-based formula.
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 15 possible allergens in soy protein, which comes from soybeans. Exactly how soy protein causes an allergic reaction is still not clear.
Certain factors may put you at greater risk of developing a soy allergy:
- Family history. You're at increased risk of allergy to soy or other foods if allergies, such as hay fever, asthma, hives or eczema, are common in your family.
- Age. Soy allergy is most common in children, especially toddlers and infants. As you grow older, your digestive system matures and your body is less likely to absorb food or food components that trigger allergies.
- Other allergies. In some cases, people who are allergic to wheat, beans (legumes), milk or other foods can have an allergic reaction to soy.
Your doctor will ask about your symptoms and may perform a physical exam to find or rule out other medical problems. He or she may also recommend one or both of the following tests:
- Skin test. In this test, your skin is pricked and exposed to small amounts of the proteins found in soy. If you're allergic, you develop a raised bump (hive) at the test location on your skin. Allergy specialists usually are best equipped to perform and interpret allergy skin tests.
Blood test.A blood test can measure your immune system's response to soy by measuring the amount of certain antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. A blood sample is sent to a medical laboratory, where it can be tested for evidence of sensitivity to soy.