Soy Allergy

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.

If you — or your child — have 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, 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

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. An allergic reaction to soy may occur after one to two weeks of starting a soy formula, and is often characterized by skin and digestive problems.

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.

The only way to prevent an allergic reaction is to avoid soy and soy proteins altogether.

Medications, such as antihistamines, may reduce signs and symptoms of soy allergies. These drugs can be taken after exposure to soy to control your reaction and help relieve discomfort.

Despite your best efforts, you may still come into contact with soy. If you have a serious allergic reaction, you may need an emergency injection of epinephrine (adrenaline) and a trip to the emergency room. If you're at risk of having a severe reaction, you may need to carry injectable epinephrine (such as an EpiPen) with you at all times.