Soy Allergies Explained: Symptoms, Triggers, And Tricks

From tofu to soy milk or vegetable broth, soy has become increasingly present in everyday food products. Unfortunately, soy is one of the eight most common allergenic foods — commonly referred to as "The Big Eight" (via the U.S. Food and Drug Administration). This means that, just like peanuts, tree nuts, milk, eggs, wheat, fish, and shellfish, it can cause allergic reactions in some people.

Per a 2020 study published in the International Journal of Molecular Sciences, food allergies happen when your body reacts to a specific food protein (also called an antigen) because, while the protein is harmless to non-allergic people, your immune system perceives it as harmful and tries to attack it. Nevertheless, the study explains that food allergies are not the same as food intolerances. Therefore, while some foods like soy can cause both an allergy and intolerance, they should not be confused with one another, seeing that their consequences are very different and should be treated accordingly.

Luckily, people with soy allergy can manage it and lead a normal life once diagnosed. Moreover, most people outgrow their soy allergy during childhood (via the Mayo Clinic). This article tells you all you need to know about soy allergy, including its treatment, potential complications you should be aware of, as well as some prevention tips.

Soy allergy is an IgE-mediated food allergy that occurs due to an adverse reaction to proteins in soy. In other words, as explained by a study published in the International Journal of Molecular Sciences, when you eat a food you're allergic to for the first time (aka when your body has its first contact with the allergen) it leads to an initial immune response that results in the production of a specific antibody called immunoglobulin E (IgE), a process known as sensitization. When you consume the allergenic food again, IgE's attack it and release a series of inflammatory compounds called histamines that trigger allergy symptoms.

The study explains that sensitization to a food allergen primarily happens through food. However, it can also occur through your skin. Some unexpected sources of soy proteins that can lead to topical sensitization to soy and trigger an allergic reaction include soaps and moisturizers, according to the Food Allergy Research & Education (FARE).

According to a review published in the journal Pediatric Clinics of North America, people with IgE-mediated food allergies show symptoms immediately or within the first two hours of being exposed to the allergen. Symptoms can range from mild to severe and affect multiple bodily systems. Per the study, some common soy allergy symptoms that affect the skin include urticaria or hives and angioedema, which are characterized by an itchy rash and swelling of the skin, respectively. Furthermore, respiratory symptoms include wheezing, worsening of asthma, runny or stuffy nose (known as rhinoconjunctivitis), and swelling of the larynx. 

As for symptoms that affect the digestive system, those usually include diarrhea, abdominal pain, nausea, vomiting, and oral itching.

For the most part, soy allergies typically lead to mild symptoms. However, the Food Allergy Research & Education (FARE) warns that there's no way to predict the severity of a reaction and that, while uncommon, life-threatening reactions such as anaphylaxis cannot be dismissed. In fact, the previous study states that severe soy allergy reactions are more common in people who also have a peanut allergy or asthma.

Soy allergy symptoms can affect multiple systems in your body, such as the skin and digestive and respiratory tracts. In addition, some people may even show different symptoms every time. Therefore, diagnosing soy allergy can sometimes be complicated, according to the American College of Allergy, Asthma, and Immunology (ACAAI).

The ACAAI explains that an allergist is the type of doctor you should consult with if you suspect you have a food allergy. During your visit, the allergist will ask detailed questions about your symptoms and soy intake, such as which food you ate, how much of it you had, which symptoms appeared, how long it took for them to manifest, and how long they lasted. Furthermore, the allergist will most likely perform some tests to get the correct diagnosis.

According to the Food Allergy Research & Education (FARE), the most common allergy diagnosis tests are the oral food challenge (OFC), skin prick test, blood test, and elimination diets. OFC and skin prick tests are performed under medical supervision. The first consists of consuming more and more doses of the suspected allergen to see whether a reaction occurs and how much you can eat before showing symptoms. The second mimics skin reactions and consists of introducing small amounts of the allergen into your skin through a small prick and waiting to see whether a small wheal is formed. In contrast, blood tests look for specific IgE antibodies in your blood, and an elimination diet allows you to see whether your symptoms disappear and reappear when you eliminate and reintroduce a specific food.

People with soy allergies must follow a soy-free diet to avoid allergic reactions (via Kids With Food Allergies). Therefore, the site recommends avoiding ingredients such as soy protein, miso, edamame, natto, soy-based milk substitutes like milk, cheese, yogurt, and ice cream, soy beans and sprouts, Shoyu sauce, soy flour, soy sauce, tamari, tempeh, tofu, kinako, Koya dofu, okara, supro, yuba, yaki dofu, and textured vegetable protein (TVP). 

Furthermore, other potential or hidden sources of soy in your diet may include Asian cuisine (like Japanese, Thai, or Chinese food), natural and artificial flavorings, vegetable broth, gum, and starch, and hydrolyzed plant and vegetable proteins (via Johns Hopkins Medicine).

In addition, due to its nutritional and organoleptic characteristics, as well as the growing demand for plant-based proteins, the use of soy has significantly increased within the food industry, and now it is present in more foods than ever in the form of soy additives, according to a 2019 study published in the journal Foods. Per the study, soy can also be present in infant formulas, creamers, processed meats, baked goods, pasta, and some high-viscosity products like gravy, spreadable cheeses, and mayonnaise.

Soy allergy is a common childhood allergy that affects about 0.4% of American infants, according to the Food Allergy Research & Education (FARE). In fact, a review published in the journal Immunology and Allergy Clinics of North America states that the peak incidence of soy allergy happens at around 2 years of age. Furthermore, because soybeans belong to the legume family along with peanuts, peas, beans, and lentils, both the review and the FARE indicate that people with soy allergy are more likely to react to peanuts, a phenomenon known as cross-reactivity — meaning that a reaction caused by one compound such as soy can also be triggered by a different yet similar one, like peanuts (via ScienceDirect). Likewise, people with soy allergies have an increased risk of being allergic to other major allergens, including milk, eggs, and tree nuts (via FARE).

In addition, a study published in Nutrients explains that infants at high risk of developing soy allergy (those with a first-degree family member with soy allergy) and infants with cow's milk allergy should avoid consuming soy formula after stopping exclusive breast-feeding to reduce the risk of soy allergy development.

As with most food allergies, soy allergy can lead to a life-threatening complication or reaction called anaphylaxis, warns the American College of Allergy, Asthma, and Immunology (ACAAI). The ACAAI explains that an anaphylactic reaction happens when the body releases an excessive amount of inflammatory chemicals upon coming in contact with an allergen, and it warns that it can develop suddenly and worsen very quickly, leading to death if left untreated.

An anaphylactic reaction may start with mild symptoms, yet it can easily put you into shock. Common symptoms of anaphylaxis include trouble breathing, tightening of the throat, swelling, nausea, vomiting, dizziness, diarrhea, abdominal pain, low blood pressure, fainting, and tachycardia or rapid heart rate. This reaction is managed using an epinephrine auto-injector, which supplies the hormone adrenaline and helps reverse life-threatening symptoms like low blood pressure and blocked airways (per ACAAI). The ACAAI notes that, when in doubt, use epinephrine right away, as its benefits outweigh the risks of having had an unnecessary dose — which include anxiety, shakiness, and restlessness.

A 2011 review published in the World Allergy Organization Journal explains that as soon as you identify an anaphylactic reaction, you should inject epinephrine immediately and call for help at the same time. It also recommends laying the person down on their back to keep them from falling and raising their legs to promote blood circulation and ensure that the injected adrenaline reaches the heart. Also, since soy allergy is more common in kids, caregivers such as parents, teachers, or nannies should be aware of how to respond in case of a life-threatening emergency, according to the Centers for Disease Control and Prevention (CDC).

According to a review published in the journal Immunology and Allergy Clinics of North America, soy allergy is more common in children — especially if they also have a peanut allergy. Nevertheless, the review points out that there have been cases of a late-onset soy allergy in which people start showing typical symptoms to soy and soy products after having consumed them as a regular part of their diet. Per the review, this is also more common in people with persistent peanut allergy (meaning that they did not outgrow it).

For instance, a 2006 review published in the journal Arerugi presented a case of a 22-year-old man who showed an itchy skin rash and three anaphylactic reactions 10 to 14 hours after consuming natto (a Japanese food made with fermented soy). Per the review, the viscous texture of natto leads to a delayed allergen absorption. Thus, natto-induced anaphylaxis — a severe allergic reaction — is of late-onset, meaning that it can appear up to half a day after ingestion. This differs from common anaphylactic reactions that can happen within minutes (via the Mayo Clinic).

As with all food allergies, soy allergy treatment focuses on eliminating all soy and soy-containing foods and products from your diet and everyday life (via Healthline). Yet, accidents may still happen, in which case there are two courses of action depending on the severity of the symptoms. Per a 2020 study published in the International Journal of Molecular Sciences, mild to moderate symptoms such as itching and hives can be resolved by taking oral antihistamines, which block the release of the inflammatory chemicals (or histamines) that are responsible for the reaction. 

However, severe allergic reactions such as anaphylaxis require adrenaline, which is typically administered in the form of an epinephrine auto-injector or EpiPen and helps prevent the progression of fatal symptoms such as shock or throat tightening.

Nevertheless, according to the study, researchers are trying out new food allergy treatment options. For instance, some are testing specific immunotherapy strategies that aim to desensitize the body to the allergen. The goal with this kind of therapy is to keep an allergic reaction from happening when a person comes in contact with the allergenic food, or at least to increase the dose or amount of food needed to trigger the reaction. Similarly, a 2017 study published in Frontiers in Pediatrics proposes the use of probiotics for food allergy prevention. Still, more research needs to be conducted.

According to the Mayo Clinic, some children eventually move beyond their food allergy, allowing them to consume the problematic food without risk. However, the chances of becoming tolerant to an allergen depend on the type of food responsible for the allergy and how severe its symptoms are. Luckily, soy allergy is among the most often outgrown food allergies, along with milk, egg, and wheat allergies. Per a review published in the journal Pediatric Clinics of North America, one study in 133 children with soy allergy found that roughly 50% of them had outgrown the allergy at 7 years old, and 69% did so at 10 years of age.

Additionally, another review published in the journal Alimentary Pharmacology and Therapeutics explains that tolerance can also be a step-by-step process. The review states that the re-introduction of foods into the diet is sometimes more successful if you start with cooked foods and then move to their raw versions. Per the review, allowing newly tolerated foods provides several benefits, including improved quality of life and easier achievement of adequate nutrition.

Suppose you experience a reaction after eating a specific food. In that case, it does not necessarily mean that you are allergic, but rather that you could be dealing with a food intolerance (per Kids With Food Allergies). The site explains that, unlike food allergies, food intolerances are not caused by a hyper-reactive immune system. Instead, they're often due to a difficulty your body may have digesting and absorbing a particular food. Therefore, symptoms often include the digestive system, and while troublesome, they're not considered fatal.

Multiple food allergies and intolerances are caused by the same food, and such is the case for soy. According to Livestrong, people with soy intolerance may experience symptoms like gas, bloating, abdominal pain, and nausea after consuming soy, which may appear as early as 30 minutes post-ingestion and up 48 hours after. Despite being two very different things, soy intolerance is treated the same way you'd treat a soy allergy, meaning that you should still avoid consuming soy and its multiple derived products.

Given that food allergies — including soy allergy — are managed through allergen avoidance, one of the most commonly recommended tips when living with a food allergy is to read food products' nutritional labels thoroughly. This is because, according to the Food Allergen Labeling and Consumer Protection Act (FALCPA), foods that contain one or more of the eight major food allergens must clearly disclaim its presence on their label to warn consumers of the potential risk (via Kids With Food Allergies). 

According to the U.S. Food and Drug Administration (FDA), FALCPA requires allergens to be identified in the ingredient list or in an additional section called "Contains," after which manufacturers must list the food source that contains the allergen.

However, FALCPA doesn't cover the presence of allergens in prescription or over-the-counter drugs, personal care items, foods in their natural state, alcoholic drinks, and restaurant or pet foods, explains Kids With Food Allergies). Therefore, according to the Cleveland Clinic, people with a soy allergy should also be mindful of non-food items that might contain soy, such as cleaning products, candles, crayons, pet foods, and certain makeup and personal hygiene items. 

Lastly, you should also check for a label that disclaims whether a product was made on a facility that shares equipment or surfaces with soy. This could also trigger a reaction due to potential cross-contamination (via the Cleveland Clinic).