What Is Soy Allergy

Soy allergy is a food allergy that causes the immune system to ‘overreact’ when soy proteins are ingested. It mainly affects infants and children. 

Read on to find out how a soy allergy and soy intolerance differ, whether a soy allergy is contagious, preventable, or treatable, what foods, drinks, and items to avoid if you have a soy allergy when to call 911, and much more! 

Introduction 

Soy allergy¹ is a type of food allergy that triggers an abnormal immune response after soy proteins are eaten or drunk. The immune system of people with soy allergies mistakes soy proteins for foreign toxic ‘invaders’ like bacteria or viruses and, therefore, causes allergic reactions throughout the body. 

Soy allergies are common,¹ especially in children and infants, causing over 0.4% of infants in the US to be allergic to soy products. 

Causes

As described briefly above, soy allergy is caused by an abnormal immune system reaction (over-reaction) to soy proteins. 

Soy allergies can cause¹ the immune system to react in two different ways:

1. Immunoglobulin E-mediated reactions (IgE-mediated reactions): as suggested by its name, this type of immune response causes the body to produce immunoglobulins (also known as ‘’antibodies’’), mainly immunoglobulin E (IgE), when soy proteins are ingested. IgE-mediated reactions to soy develop very quickly and can lead to anaphylaxis, which is a severe allergic reaction that is fatal if not treated promptly. 
2. Non-immunoglobulin E-mediated reactions (Non-IgE-mediated reactions): in contrast to IgE reactions, non-IgE-mediated reactions cause the immune system to ‘overreact’ when exposed to soy, but without producing or releasing IgE. As such, non-IgE-mediated reactions develop slower than IgE reactions (up to 48 hours) when soy proteins are ingested. 

Non-IgE-mediated reactions are also not as life-threatening as IgE-mediated reactions and can lead to soy protein intolerance or eosinophilic esophagitis (EoE). EoE causes the oesophagus (a muscular hollow tube that connects the mouth to the stomach) to become inflamed due to an excess of certain white blood cells called eosinophils. 

Signs and symptoms 

The main signs and symptoms¹ of soy allergies include: 

• Hives: raised, red, itchy bumps (welts) on the skin 
• Stomach cramps
• Nausea
• Vomiting
• Diarrhea
• Indigestion
• Coughing
• Itching
• Eczema (atopic dermatitis): a skin condition characterised by very dry, flaky, itchy, cracked, and inflamed skin. Anaphylaxis: causes breathing difficulties, increased heart rate, low blood pressure, dizziness, confusion, etc. 

Diagnosis

An allergist or healthcare provider who specialises in food allergies will diagnose¹ a suspected patient with a soy allergy by performing a series of tests in the following order:

1. Physical examination and medical history: prior to conducting soy allergy tests, the allergist will assess the patient’s symptoms and check to see whether there is any family history of food allergies or whether the patient has been diagnosed with food allergies in the past. 
2.  Allergy tests: based on the patient’s signs, symptoms, and medical and family history, the allergist may request either of the following tests to be performed to assess how the patient’s immune system reacts to soy proteins:
   • Blood test: using a thin needle that is almost identical to the size of an earring, the allergist will take a small blood sample from a vein in the patient’s arm and send it to a laboratory for testing. The lab will add soy proteins to the blood sample and measure the level of IgE antibodies in it. Results from the blood tests are usually provided within a week or longer. 
   • Skin prick (patch) test: before performing this test, the allergist will sterilise the patient’s forearm or upper back with iodine or alcohol.

There are different ways in which the test can be performed, either via a ‘’skin prick’’ or ‘’skin patch’’, hence the name of the test. 

In the first method, the allergist will use a thin needle (lancet) to ‘prick’ the patient’s skin with liquid containing soy proteins. 

In the second method, the allergist will add a droplet of liquid containing soy proteins onto the patient’s skin and then use a lancet to ‘scratch’ the skin, thus enabling the droplets to enter the skin via the scratch. After 15 minutes of conducting the test, the allergist will then measure any discoloured spots on the patient’s skin using a ruler. 

If the allergist finds inconsistencies between the patient’s family history of food allergies and the results produced from the skin prick (patch) test, further tests may be performed, particularly the ’’graded oral challenge’’ test.1 The graded oral challenge test helps confirm the diagnosis of food allergies, including soy allergies. 

In a ‘’graded oral challenge’’ test, patients will ingest soy proteins and gradually increase the amount they consume over a 4-hour time span under the supervision of an allergist. 

Management and treatment options

The main way to treat or manage the signs and symptoms of a soy allergy¹ is by:

1. Avoiding soy altogether: the types of foods and drinks that should be avoided are provided in the 3rd FAQ below. However, in addition to soy-containing food or drink products, people with soy allergies should also avoid the following:
   • Non-food items: for example, this includes:
     • Crayons
     • Candles
     • Cleaning products
     • Pet foods
     • Synthetic fabrics
     • Certain makeup and toiletry products
   • Shared equipment: some items, whether foods or otherwise, may come into contact (cross-contamination) with soy products during the manufacturing process. Therefore, patients with soy allergies are advised to look for labels containing words along the lines of: ‘’made on equipment shared with soy’’. 
2. Using an EpiPen® medication: ‘’Epinephrine auto-injector’’ or as it is commonly known, EpiPen® is an injection medication that contains the neurotransmitter epinephrine (or adrenaline), which increases blood pressure and helps muscles relax, thus helping reverse the symptoms of anaphylaxis. 

FAQs

1. Is soy allergy contagious?

Fortunately, no.¹ Soy allergies cannot be spread from one person to another. 

2. Is soy allergy fatal? 

The prognosis¹ or outlook of people living with soy allergies very much depends on how severe their signs and symptoms are and how badly their immune system reacts to soy when it is exposed to it. 

If not managed properly and soy products are accidentally ingested by those with severe soy allergies, death can occur (from anaphylaxis). However, with caution and support from family, friends, and healthcare providers, people with soy allergies can live normal, healthy lives. 

3. What foods or drinks should I avoid if I have a soy allergy?

Avoid the following foods and drinks¹ if you have been diagnosed with a soy allergy by an allergist: 

• Soy flour
• Soy fiber
• Soy albumin
• Soy grits
• Soy non-dairy alternatives: e.g. soy milk, soy yoghurt, soy ice cream, soy cheese etc. 
• Soybean 
• Soy protein: isolate, hydrolysed, or concentrate 
• Soy nuts and soy sprouts
• Soy sauce and tamari 
• Tofu
• Tempeh 
• Textured vegetable protein (TVP)
• Edamame beans
• Miso 
• Natto
• Hoisin 

Soy may also be found in certain nut butter, vodka, vegetable broths, vegetable starches, and vegetable gums, and it is, therefore, imperative that people with soy allergies check the labels of everything they purchase, food and drink, or otherwise. 

4. What is the difference between a soy allergy and a soy intolerance?

Soy allergy¹ is when the immune system reacts abnormally to soy proteins. 

Soy intolerance¹ is when the digestive system faces difficulty breaking down or digesting soy proteins, leading to uncomfortable gastrointestinal (GI) symptoms, including gas, diarrhoea, and abdominal pain. 

Therefore, soy allergies and soy intolerances mainly differ in that soy allergies involve an abnormal immune response, whereas soy intolerances do not. 

5. When should I see a doctor if I have an allergic reaction to soy?

See a doctor¹ immediately if you:

• Have signs and symptoms of a soy allergy.
• Develop signs and symptoms as soon as you ingest soy products. 

6. When should I visit the ER if I have an allergic reaction to soy?

Visit the ER or call 911¹ at once if you:

• Develop symptoms of anaphylaxis: e.g. slow to low breathing, increased heart rate, low blood pressure, dizziness, confusion, etc. 

Summary 

Soy allergy is a food allergy that causes the immune system to ‘overreact’ when soy proteins are either eaten or drunk because they are ‘mistaken’ for harmful invaders like bacteria or viruses, for example. It mainly affects infants and children. 

Soy allergy should not be confused with soy intolerance, which is caused by an inability of the digestive symptom to digest soy proteins, thus leading to uncomfortable GI issues, including bloating, gas, diarrhea, etc. 

Soy allergy causes allergic reactions that either involve IgE antibodies (IgE-mediated reactions) or other components of the immune system (non-IgE-mediated reactions). Typically, IgE-mediated reactions develop faster and cause more life-threatening symptoms (e.g. anaphylaxis) compared to non-IgE-mediated reactions (e.g. GI issues). 

The signs and symptoms of soy allergy range from mild to severe, with the most common mild symptoms being GI issues and the more severe being hives, vomiting, and anaphylaxis. Anaphylaxis is a severe medical condition that is fatal if not treated immediately. 

At present, a soy allergy is diagnosed by an allergist mainly via a physical examination, family, and medical history check-up, as well as allergy tests (e.g. blood tests or skin prick (patch) tests), and/or graded oral challenge tests. 

The main way to treat and manage the signs and symptoms of a soy allergy is by:

• Avoiding soy: in both food and non-food items 
• Using an epinephrine auto-injector (‘’EpiPen’’) medication to prevent or reverse anaphylaxis  

See a doctor if you:

• Develop signs and symptoms of soy allergy every time you ingest or come into contact with soy products 

Visit an ER or call 911 immediately if you:

• Experience symptoms of anaphylaxis: e.g. increased heart rate, difficulty breathing, low blood pressure, nausea, confusion, etc.