For most people, soy allergy is uncomfortable but not serious. Rarely, however, 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 hours after eating a food containing the allergen.

Soy allergy symptoms can include:

• Tingling in the mouth

• Hives; itching; or itchy, scaly skin (eczema)

• Swelling of the lips, face, tongue and throat, or other body parts

• Wheezing, a runny nose or breathing difficulty

• Abdominal pain, diarrhea, nausea or vomiting

• Skin redness (flushing)

A severe allergic reaction (anaphylaxis) is rare with a soy allergy. It's more likely to occur in people who also have asthma or who are allergic to other foods besides soy, such as peanuts.

Anaphylaxis causes more-extreme signs and symptoms including:

• Difficulty breathing, caused by throat swelling

• Shock, with a severe drop in blood pressure

• Rapid pulse

• Dizziness, lightheadedness or loss of consciousness

An immune system reaction causes food allergies. With a soy allergy, your immune system identifies certain soy proteins as harmful, triggering the production of immunoglobulin E (IgE) antibodies to 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 a runny nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, difficulty breathing, and anaphylactic shock.

Food protein-induced enterocolitis syndrome (FPIES)

A food allergen can also cause what's sometimes called a delayed food allergy. Although any food can be a trigger, soy is one of the more common in children. The reaction, commonly vomiting and diarrhea, usually occurs within hours after eating the trigger, rather than minutes.

Unlike some food allergies, FPIES usually resolves over time. As with typical soy allergies, preventing a reaction involves avoiding foods with soy.

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 other 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.

• Other allergies. In some cases, people who are allergic to wheat, beans (legumes), milk or other foods can also have an allergic reaction to soy. Also, people who are allergic to soy may have test results showing allergy to other legumes, but may be able to eat them with no problem.

If you're not nursing, ask your doctor for advice on what to feed your child until your appointment to reduce the risk of symptoms.

If you have symptoms of soy allergy, avoid foods that contain soy.