What Are the Signs of an Allergic Reaction to Soy?

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  • Written By: C. K. Lanz
  • Edited By: O. Wallace
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  • Last Modified Date: 18 October 2019
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The most common signs of an allergic reaction to soy include hives, itching, and swelling of the facial area, tongue and throat, or other areas of the body. Gastrointestinal pain, tingling in the mouth, or difficulty breathing are other typical signs. In most cases, an allergy to soy is not serious but may be uncomfortable. Rarely, an individual may suffer a severe reaction to soy called anaphylaxis. Anaphylaxis is a medical emergency that often causes shock, rapid pulse, and airway constriction that makes it almost impossible to breathe.

For most people, the symptoms of a soy allergy are annoying but not life threatening. Many people experience gastrointestinal problems like vomiting, nausea, and stomach pain. The mouth may tingle or the skin may itch, develop hives, or flush. Parts of the body can swell and the person consuming soy may wheeze or experience a runny nose and trouble breathing.

Anaphylaxis is a severe allergic reaction to soy that is rare but more likely in people with other food allergies or asthma. This is a medical emergency that often causes a swollen throat that impedes breathing, shock, and full-body flushing. Rapid pulse, lightheadedness and a quick drop in blood pressure are other symptoms of anaphylaxis.


The symptoms of an allergic reaction to soy usually manifest within a few minutes to several hours after eating a food product that contains soy. Soy may appear on a product label as soya, soybeans, glycine max, or edamame. Tofu, miso, and tempeh are products with soy as a main ingredient.

Hidden sources of soy include hydrolyzed and textured vegetable protein, lecithin, and Vitamin E. Vegetable oil and monosodium glutamate are other common but hidden sources of soy protein. People with a soy allergy can also look for the wording, “contains soy” on the label when in doubt.

An allergic reaction to soy typically manifests for the first time during infancy when a child reacts to soy-based infant formula. The majority of children with this food allergy will eventually outgrow it, but in some cases it will continue into adulthood. Breast-feeding for the first four months or using a milk-based formula may help reduce the risk of food allergies generally.

Like all food allergies, an allergic reaction to soy is caused by an immune system reaction. The immune system mistakenly determines that soy proteins are harmful and produces antibodies. The next time soy is introduced into the body, these soy protein antibodies trigger the immune system to release histamine. Histamine in addition to other chemicals, causes the symptoms of an allergic reaction to soy.

Diagnosing a soy allergy usually involves consuming the suspected allergen and monitoring the individual for a reaction. A doctor may also perform a skin test during which the skin is pricked and exposed to a small amount of soy protein. A person allergic to soy protein will develop a hive at the site of exposure. A blood test that detects the amount of soy protein antibodies in the bloodstream is also available.

Those with a soy allergy have to avoid all soy products in order to prevent an allergic reaction. This can be challenging given the pervasive use of soy in food products like meats, chocolate, and bakery items including nearly all bread products available in the United States. Many breakfast cereals also contain soy proteins. Fortunately, most people with a soy allergy can tolerate a small to moderate amount of the protein.

Antihistamines can lessen the symptoms but do not cure the allergy. Individuals at risk for anaphylaxis may have to carry injectable epinephrine and wear a medic alert bracelet at all times. If such individuals come into contact with soy or a soy protein, they may need to be injected immediately and seek emergency medical treatment.


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