Allergies to soy are common. They often start in infancy with an allergic reaction to soy-based infant formula. Most children outgrow a soy allergy by age 10, but in some people, the allergy continues into adulthood.

Symptoms of soy allergy include a tingling in the mouth, hives or itchy, scaly skin. The lips, face, tongue, throat or other body parts may swell. Other symptoms include a runny nose, wheezing, breathing difficulty, skin redness, abdominal pain, diarrhea, nausea or vomiting.

Fortunately, for most people, a soy allergy typically is uncomfortable but not serious. But for others it can be severe, even life-threatening, causing anaphylaxis. The signs and symptoms usually start within a few minutes to hours after eating a food containing soy.

Related: Should Your Daughter Eat Soy?

If you suspect an allergy to soy, you can ask your doctor to check you or your child for it. Tests include a skin prick test and a blood test. In the skin test, the skin is pricked and small amounts of proteins found in soy are deposited. You develop a hive at the test site if you are allergic. Blood tests look for antibodies produced by your immune system in response to the soy.

Hidden sources of soy

Soy is one of the eight allergens that are covered under a labeling requirement of the Food Allergen Labeling and Consumer Protection Act of 2004. In other words, soy must be clearly listed on a product label.

Soy is in many, many foods, even those you would not think contain it. According to the Mayo Clinic, the American College of Allergy, Asthma & Immunology (ACAAI) and Stanford University's Lucile Packard Children's Hospital, here are some common foods that may contain soy:

  • Canned tuna
  • Canned meat
  • Deli meat
  • Baked goods (including packaged cakes and cookies)
  • Chocolate
  • Crackers
  • Cereal
  • Energy bars
  • Chicken nuggets
  • Low-fat peanut butter
  • Canned soups
  • Vegetable oil, vegetable gum, vegetable broth or vegetable starch 
  • Worcestershire sauce
  • Hot cocoa mixes
  • Fruit drink mixes
  • Malt beverages
  • Salad dressings
  • Imitation bacon bits

Ask your doctor what foods might be safe for you. For instance, most people who have soy allergies can eat highly refined  soybean oil, according to the ACAAI. But don't try it until you get a doctor's OK. Soy lecithin, a mixture of fatty substances extracted from soybeans and used in many foods and for other applications, may also be safe. But again, don't guess. Ask your allergist.

Related: Hidden Food Allergens: 18 Surprising Foods (and Drinks) That Have Them

Of course, avoid these more obvious sources of soy, too:

  • Soy milk or cheese
  • Soy ice cream or yogurt
  • Soy flour
  • Tofu
  • Miso
  • Natto
  • Shoyu (soy sauce)
  • Tempeh
  • Soy sauce
  • Edamame

Other words to look for on the label that may indicate soy is in the food:

  • Glycine max
  • Hydrolyzed vegetable protein or HVP
  • Mono-diglyceride
  • Monosodium glutamate (MSG)
  • Textured vegetable protein or TVP

Related: Allergic to Eggs? Avoid These Hidden Sources

Tips for the soy allergic

Besides reading labels, you can take other measures to minimize the risk of a reaction to soy.

Wear an allergy alert bracelet. Ask your doctor if you or your child should consider this bracelet. It will help paramedics in case you lose consciousness in the midst of an attack.

When eating out, talk to the waiter. Be sure the waiter knows you or your child has a soy allergy. Ask if the dish you have in mind has soy as an ingredient. If the waiter seems unsure, order something else.

Ask about carrying an epinephrine autoinjector for you or your child. Use it as your doctor directs, usually at the first sign that you or your child is having an allergic reaction.

Be sure friends and family are informed. They should know to call 911 for an ambulance if you or your child is having a severe reaction. You need this medical help even if you used the autoinjector.

Related: What to Put in Your Home First Aid Kit

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.