What Is a Soy Allergy?

When someone is allergic to soy, the body's immune system, which normally fights infections, overreacts to proteins in soy. If the person eats something made with soy, the body thinks these proteins are harmful invaders and responds by working very hard to fight off the invader. This causes an allergic reaction.

Soy is a common food allergy. Soy comes from soybeans, which are in the legume family (along with beans, lentils, peas, and peanuts). Some people are allergic to just one type of legume; others are allergic to more than one.

Allergy to soy is more common in infants and kids than teens and adults, but can develop at any age.

What Are the Signs & Symptoms of a Soy Allergy?

When someone with a soy allergy has something with soy in it, the body releases chemicals like . This can cause symptoms such as:

• wheezing
• trouble breathing
• coughing
• hoarseness
• throat tightness
• belly pain
• vomiting
• diarrhea
• itchy, watery, or swollen eyes
• hives
• red spots
• swelling
• a drop in blood pressure, causing lightheadedness or loss of consciousness (passing out)

Allergic reactions to soy can differ. Sometimes the same person can react differently at different times. Some reactions to soy are mild and involve only one system of the body, like hives on the skin. Other times the reaction can be more severe and involve more than one part of the body.

Rarely, soy allergy can cause a severe reaction called anaphylaxis. Anaphylaxis might start with some of the same symptoms as a less severe reaction, but can quickly get worse. The person may have trouble breathing or pass out. More than one part of the body might be involved. If it isn't treated, anaphylaxis can be life-threatening.

How Is an Allergic Reaction to Soy Treated?

If your child has a soy allergy (or any kind of serious food allergy), always keep two epinephrine auto-injectors available in case of a severe reaction.

An epinephrine auto-injector is a prescription medicine that comes in a small, easy-to-carry container. It's easy to use. Your doctor will show you how. Kids who are old enough can be taught how to give themselves the injection. The epinephrine should be nearby, not left in a locker or in the nurse's office.

The doctor can also give you an allergy action plan, which helps you prepare for, recognize, and treat an allergic reaction. Share it with anyone who takes care of your child, including relatives, school officials, and parents at play dates. Also consider having your child wear a medical alert bracelet.

Every second counts in an allergic reaction. If your child starts having serious allergic symptoms, like swelling of the mouth or throat or difficulty breathing, give the epinephrine auto-injector right away. Also give it right away if the symptoms involve two different parts of the body, like hives with vomiting. Then call 911 and take your child to the emergency room. Your child needs to be under medical supervision because even if the worst seems to have passed, a second wave of serious symptoms can happen.

Sometimes allergists recommend also carrying over-the-counter (OTC) , as these can help treat mild allergy symptoms. Use an antihistamine after — not as a replacement for — the epinephrine shot during a life-threatening reaction.

What Else Should I Know?

If your child has a soy allergy, help them avoid eating anything that has soy in it. Read food labels carefully because ingredients can change, and soy can be found in unexpected places.

Some foods look OK from the ingredient list, but while being made they can come in contact with soy. This is called cross-contamination. Look for advisory statements such as "May contain soy," "Processed in a facility that also processes soy," or "Manufactured on equipment also used for soy." Not all companies label for cross-contamination, so if in doubt, call or email the company to be sure.

When eating away from home, make sure your child always has two epinephrine auto-injectors with them that haven’t expired. Also, tell the people preparing or serving your child's food about the soy allergy. Sometimes, you may want to bring food with you that you know is safe. Don't eat at the restaurant if the chef, manager, or owner seems uncomfortable with your request for a safe meal.

Also talk to the staff at school about cross-contamination risks for foods in the cafeteria. Some families feel most comfortable packing lunches from home.

For more about managing food allergies, visit:

• Food Allergy Research & Education (FARE)