Soy Allergies: What You Need to Know

A soy allergy is an abnormal response of the body to soybeans or soy products. Soy is a common ingredient in many processed foods, such as infant formulas. Products like soy milk and soy sauce are common triggers of a soy allergy.1,2

What can trigger a soy allergy?

Soy can be found in many food products, sometimes under different names. Common soy products include:1-3

  • Soybean
  • Soy milk, ice cream, cheese, or yogurt
  • Soya
  • Soy nuts and soy sprouts
  • Many Asian foods, such as soy sauce, miso, edamame, hoisin, or tofu
  • Some infant formulas
  • Some processed meats or hot dogs
  • Some energy bars
  • Some baked goods
  • Some low-fat peanut butters or nut butters
  • Some canned foods such as soups or tuna
  • Some vodkas

Studies have shown that most people with a soy allergy can safely eat foods containing a food additive called soy lecithin. If you have a soy allergy, speak with your allergist to find out if you can safely have products with soy lecithin.1

Soy allergy symptoms

People who are allergic to soy may have an allergic reaction if they eat or come into contact with soy or soy products. Symptoms of a soy allergy include:1

  • Vomiting
  • Diarrhea
  • Stomach cramps or indigestion
  • Wheezing or coughing
  • Difficulty breathing
  • Throat tightness or hoarseness
  • Weak pulse
  • Pale or blue skin
  • Swelling, often of the tongue or lips
  • Hives
  • Dizziness
  • Confusion

Who can develop a soy allergy?

Studies estimate that between 0.1 and 1.1 percent of people have a soy allergy. Soy is a common food allergen in children, but it is less common in adults.4,5

Although soy allergy appears most often in infants and children, it can develop at any age. It can also be caused by foods a person had eaten before without an allergic reaction. Many children grow out of a soy allergy.1,3

How do doctors diagnose a soy allergy?

Diagnosing soy allergies can be difficult. Allergic reactions to soy can affect multiple organs in the body, such as the skin and lungs. Symptoms also vary from person to person. The same person may not even have the same symptoms each time.1

To diagnose a soy allergy, a doctor that specializes in allergies (allergist) may conduct several tests. This includes asking questions about your diet and your history of allergy symptoms. Questions may include:1

  • What did you eat?
  • How much did you eat?
  • What were your symptoms?
  • How long did your symptoms last?

The doctor may also perform a test known as a "skin-prick" test. In this test, a drop of liquid containing soy is placed on your skin. A small probe is then used to pierce the skin and allow the liquid to enter the body. If the person is allergic to soy, a small bump develops at the site.1

The doctor may also perform a blood test to see whether food-specific antibodies are present in your blood. Your immune system makes antibodies to fight foreign substances.1

These tests are helpful to diagnose a soy allergy, but they do not predict how severe an allergic reaction could be.1

Managing a soy allergy

The best way to manage a soy allergy is to avoid products containing soy. This requires reading labels carefully, as soy products can have different names.1

Always be prepared to treat an allergic reaction. These reactions are difficult to predict and can be severe. An allergist may provide you with an epinephrine injector and show you how to use it. Epinephrine is a prescription drug used to treat anaphylaxis, a severe allergic reaction that affects many systems in the body.1

If you have a soy allergy, always make sure you have your epinephrine injector with you and that it is not expired. Your doctor may also suggest carrying two doses with you in case of a severe reaction.1

What to do if you have a severe allergic reaction

If you experience severe soy allergy symptoms or anaphylaxis, use your epinephrine injector immediately. Severe symptoms include:1

  • Shortness of breath
  • Difficulty breathing
  • Throat tightness
  • Weak pulse
  • Rash or hives that appear along with stomach upset or pain

If you are unsure whether the reaction is severe, use the epinephrine injector anyway. The possible benefits outweigh the risks of an unnecessary dose.1

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