Soy allergy in babies

Soy allergy: the basics

Soy comes from soybeans, a member of the legume (bean) family. It’s in some infant formulas and in many processed foods. ACAAI says soy is one of the most common food allergens in young children, and reactions usually first appear in babies and children under 3. It happens when the immune system overreacts to proteins in soy.

The good news: many children outgrow it during childhood (ACAAI). One study of 133 children seen at a specialist allergy clinic estimated that about 45% had outgrown soy allergy by age 6 and 69% by age 10. Most of those children also had peanut allergy, so the figures come from one specialist clinic and may not apply to every child. Your allergist will tell you if and when to check again.

In the US, soy is one of the 9 major food allergens. In the UK, soya is one of the 14 allergens food businesses must tell you about.

Introducing soy

Soy can go in with your baby’s other first foods, from around 6 months. The NHS lists soya among the foods that can trigger allergy and can be introduced from around 6 months, one at a time, so you can spot any reaction. The AAP lists soy with egg, peanut, dairy and the other allergens to offer once your baby has managed a few lower-risk first foods.

Good first forms:

• soft or silken tofu, mashed and served on a pre-loaded spoon, or firm tofu in soft, finger-length strips
• plain, unsweetened soy yogurt
• cooked edamame, mashed or blended. Never whole: the CDC lists whole beans as a choking hazard.
• soft-cooked tempeh, crumbled finely into a food your baby already eats

Offer the first taste on a day your baby is well, at home, when you can watch them for a couple of hours afterward. Start with a small amount, and if there’s no reaction, build up over the next few servings. Then keep soy in your baby’s diet: see keeping allergens in the diet.

Talk to your doctor first if your baby has severe eczema, an egg allergy, or has already reacted to a food (AAP). Ask how and when to introduce soy and the other allergens, not about putting them off.

Signs of soy allergy

Reactions usually start within minutes of eating, but can take up to 2 hours (NHS).

Mild to moderate (ACAAI, NHS):

• hives or a red, itchy rash
• mild puffiness of the face or around the eyes
• vomiting once, tummy pain or diarrhea
• sneezing, or a stuffy or runny nose

If it’s only one of these, stop offering soy, stay with your baby and watch them closely for the next couple of hours, and call your pediatrician before you try it again. If signs show up in more than one part of the body at once, treat it as anaphylaxis (below).

Signs of anaphylaxis are trouble breathing, wheezing or a cough that won’t stop, swelling of the tongue or throat, lips or mouth that suddenly swell, a hoarse cry, turning pale or floppy, becoming very sleepy or unresponsive, or signs in more than one part of the body at once. If you see any of these and your baby has an epinephrine (adrenaline) auto-injector, use it right away, then call for an ambulance. Call 911.Call 999.Call your local emergency number (such as 112 in Europe or 000 in Australia). If you don’t have an auto-injector, call straight away. Keep your baby lying down, never standing or walking (on their side if they’re vomiting, head and shoulders a little raised if breathing is hard), and go to hospital even if they seem better. See signs of anaphylaxis.

ACAAI says anaphylaxis from soy is rare, but it can happen.

Soy and FPIES

Soy can also cause a different, delayed kind of reaction called FPIES. ACAAI lists soy, along with cow’s milk, as one of the most common triggers, especially in infant formula. Instead of hives, a baby vomits again and again, starting a few hours after eating, and may turn pale or floppy. The usual allergy tests are typically negative (ACAAI). If your baby vomits once or twice a few hours after soy and is alert and like themselves, call your pediatrician or GP. Call 911 or go to the emergency room if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake.Call 999 or go to A&E if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake.Call your local emergency number (such as 112 in Europe or 000 in Australia) or go to the emergency department if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake. See FPIES.

How soy allergy is diagnosed

Your doctor or an allergist will ask what your baby ate, how much, how long before symptoms started, and what they were. They may arrange a skin prick test or a blood test for IgE to soy. ACAAI says neither test is conclusive on its own: a positive result doesn’t always mean a child will react. If the results aren’t clear, the allergist may suggest an oral food challenge, where your child eats small, increasing amounts of soy under strict supervision, with emergency medicine on hand. Don’t try a challenge at home.

Oral food challenges are also how an allergist checks whether a child has outgrown soy allergy (ACAAI). Don’t offer soy again at home to “see” until your allergist says so.

Living with soy allergy

Until your allergist tells you otherwise, avoid soy completely, and read labels every time.

• US labels. Soy must be named in plain language on packaged foods, either in the ingredient list, for example “lecithin (soy)”, or in a “Contains” statement (FDA). “Soy”, “soya” and “soybean” all count (FDA).
• UK labels. Soya must be emphasized in the ingredients list, for example in bold (GOV.UK).
• Where soy turns up. ACAAI lists some infant formulas, canned broths and soups, canned tuna, processed meats and hot dogs, baked goods, chicken nuggets, some nut butters and many Asian dishes. Soy milk, soy yogurt, edamame, miso, tempeh and tofu are all soy.
• Soybean oil and soy lecithin. Highly refined oils are exempt from US allergen labeling (FDA), and ACAAI says most people with soy allergy can eat highly refined soybean oil and often soy lecithin. Ask your allergist before you rely on this.
• Shared frying oil. Food fried in oil that was used for a soy food can pick up soy protein (ACAAI).
• “May contain” labels are voluntary in both countries (FDA, GOV.UK). Ask your allergist how to treat them.

If your baby has formula, a soy-based formula is not an option. Ask your pediatrician or GP which formula to use.

Soy, peanut and tree nuts

Soy and peanut are both legumes, so parents often ask whether a soy allergy means avoiding peanut too. ACAAI says not necessarily: they are separate foods with unrelated allergens, and children allergic to soy are no more likely to be allergic to peanut or tree nuts than to another food. Some children do have more than one food allergy, so ask your allergist how and when to introduce peanut and the other allergens, rather than holding them all back. See how to introduce peanut.

When to see a doctor

Call your pediatrician or GP if:

• your baby has had any reaction to soy, even a mild one
• your baby has vomited once or twice, or has diarrhea, hours after soy formula or soy foods and seems alert and like themselves
• you think your baby has a soy allergy and want to know about formula, other legumes or other allergens

Don’t cut soy or other major foods out on your own: the NHS says to talk to your health visitor or GP, who may refer you to a dietitian.

Where US and UK advice differs

• The name. “Soy” in the US, “soya” in the UK. Both appear on labels.
• How labels show it. US packaged foods name soy in the ingredients or a “Contains” statement (FDA). UK labels emphasize soya in the ingredients list, and loose food sellers must tell you if you ask (GOV.UK).
• Who should check first. The NHS asks you to talk to your GP or health visitor before introducing allergens if your baby has eczema or a food allergy, or there’s a family history of food allergies, eczema, asthma or hay fever. US guidance singles out severe eczema and egg or other food allergy.

For the other allergens, see how to introduce allergens and the safe first form of each one.