Credit...Angie Wang

The New Rules of Food Allergy Prevention, Testing and Diagnosis

Food allergies can be scary. Here’s how to reduce your baby’s risk, understand allergy tests and respond to a reaction if it happens.

This guide was originally published on Aug. 9, 2019 in NYT Parenting.

For kids and their families, food allergies change everything, from birthday parties and eating out to school snacks and sporting events. “There’s so much fear and anxiety, because food is part of everything kids do,” said Dr. Ruchi Gupta, M.D., M.P.H., a professor of pediatrics at Northwestern Medicine and the Ann and Robert H. Lurie Children’s Hospital of Chicago. Dr. Gupta’s research has estimated that about 8 percent of children in the United States — some 5.6 million kids — have a food allergy. And Dr. Gupta knows how a food allergy can impact everyday life, because her daughter is one of those 5.6 million kids.

In recent years, new scientific discoveries have brought hope of reducing these numbers. The 2015 publication of the Learning Early About Peanut Allergy, or LEAP, study showed that introducing peanut products (such as peanut flour, peanut butter or peanut puffs) to infants between 4 and 11 months of age, rather than delaying introduction to age 5, reduced peanut allergy by 81 percent in kids considered high-risk for developing allergies. The prospect of preventing allergy is exciting, but it also means navigating the new rules of when (and how best) to introduce allergenic foods; as well as how to test and diagnose your child while they’re still a baby.

To help walk you through the process, I talked with three pediatric allergists, one pediatrician and one registered dietitian, all of whom are also allergy researchers

“A food allergy is really a reproducible immunologic response to a food,” said Dr. Corrine Keet, M.D., Ph.D., an associate professor of pediatrics at Johns Hopkins University School of Medicine. This commonly means that your immune system overreacts to a food and produces a type of antibody called IgE, which in turn triggers “immediate symptoms that include rash, vomiting, breathing problems and sometimes anaphylaxis,” said Dr. Keet.

The nine most common foods that cause allergies in children through age 17 — from most to least common — are peanuts, milk, shellfish, tree nuts, eggs, fish, wheat, soy and sesame. We know the most about prevention of peanut allergy, so that’s the focus of current guidelines. Other food allergies may develop in the same way, but much more research is needed.

According to the National Institute of Allergy and Infectious Diseases, or NIAID, if a person’s immune system is making antibodies specific to a given food component, it means they’re sensitized to that allergen. Sensitization is just one step on the way to developing an allergy, and it doesn’t always progress to one. A person can produce antibodies to a food, yet still be able to safely eat that food without any signs of a reaction; an allergy can only be definitively diagnosed if there’s a reaction every time the food is eaten.

On the other hand, “there are a lot of different things that can happen when we eat that are not what we consider to be food allergies,” Dr. Keet said. For example, skin irritation from contact with acidic foods is common in babies. Lactose intolerance, which is caused by an inability to fully digest a sugar contained in dairy foods and which can lead to discomfort like gas and bloating, can develop in childhood. Neither are food allergies, because they don’t involve immune responses.

In 2017, the government released new guidelines in response to the LEAP study, outlining which babies are at highest risk for peanut allergy and, depending on that risk level, how parents can go about introducing peanut products to reduce their baby’s risk of developing an allergy.

“Babies who have persistent moderate to severe eczema, usually starting early in infancy, are really those that are at the highest risk to develop food allergies,” said Dr. David Stukus, M.D., an associate professor of pediatrics at Nationwide Children’s Hospital. Eczema causes inflamed, dry and scaly skin. It’s common in babies, but only 5 to 10 percent of cases are severe (meaning it covers most of the body and doesn’t get better with creams or topical steroids), Dr. Stukus said.

Researchers believe that when eczema causes small cracks in the skin, tiny food components can enter and prompt the immune system to begin producing antibodies specific to that food, Dr. Stukus said. Several small randomized trials have found that parents who applied an emollient moisturizer to their infants’ skin each day for the first 6 to 7 months had babies who were less likely to develop eczema than parents who didn’t. More studies are underway to see if moisturizing might translate to lowered food allergy risk. In the meantime, a daily rubdown won’t hurt. “It’s cheap … there’s virtually no downside, it’s great bonding,” Dr. Stukus said. On the other hand, he said there’s an internet myth that rubbing peanut butter on your baby’s skin might prevent allergy. “That’s a bad idea,” he said; it’s more likely to cause an allergy.

The government guidelines say that babies who have already been diagnosed with an egg allergy are also considered high-risk for peanut allergy. Dr. Keet said she extends this category to babies with cow’s milk allergy or who have any other food allergy.

For a baby, having an older sibling or parent with a food allergy “certainly increases the risk, but probably not by a very substantial amount,” Dr. Keet said. Still, if your previous experience with allergy makes you anxious about feeding your baby, talk through your concerns with your pediatrician or an allergist so you have a path forward for introducing allergens, because early introduction is the best way to reduce your baby’s risk of food allergies.

Most babies don’t need to be screened for food allergy at all, said Dr. David Fleischer, M.D., section head of allergy and immunology at the University of Colorado Denver School of Medicine. Government guidelines recommend that only those who are considered high-risk be screened before trying to eat peanut products, but even this is controversial in the international food allergy community. Australia’s recent guidelines, for instance, don’t recommend pre-emptive screening of these high-risk groups at all.

The problem with screening babies before they have symptoms is that allergy tests can indicate only whether they are producing antibodies against an allergen, but this doesn’t mean they have a true food allergy. If a positive test is erroneously used to diagnose a food allergy and parents are told to avoid feeding their child that food, dietary restriction might not only be unnecessary, but could cause an allergy to develop, Dr. Stukus said. “That is absolutely heartbreaking because that is now a medical professional absolutely causing harm to somebody else and creating an allergy that did not exist before,” he said. If your baby does have any allergy testing, how the results are interpreted is key, and you don’t want it to unnecessarily delay introduction of foods.

If you have a high-risk baby, your pediatrician or allergist might run a blood test to measure peanut-specific antibodies. If the test is negative, you can be reassured that a peanut allergy is unlikely and go ahead and introduce it. If it’s positive, you should see an allergist for more testing, Dr. Fleischer said.

An allergist might do a skin prick test, which involves placing a tiny amount of a food protein under the skin, and watching for a reaction in the form of a raised, puffy “wheal.” A very big wheal means that your child is more likely to have an allergic reaction, but it’s also not a perfect test. The only way to truly diagnose food allergy is to see what happens when your baby eats the food, and more and more allergists are doing “food challenges” with babies in their offices, where they offer small amounts of the food and carefully monitor for signs of a reaction, with the capability to treat the child if necessary.

As an example, Dr. Fleischer said he once saw a very large wheal after a peanut skin test on an 8-month-old patient with severe eczema. The wheal was big enough that many allergists might have simply diagnosed it as a peanut allergy. But Dr. Fleischer gave the baby a food challenge with a small amount of peanut, and he didn’t react. He told the parents to continue regularly feeding him peanuts at home, and the child, who was 3 at his last appointment, can now completely tolerate peanuts. Dr. Fleischer thinks it’s likely this child would have developed an allergy without this exposure, given his eczema and reactive skin test.

Government guidelines recommend that if your baby is high-risk (if they have severe eczema or an egg allergy), you should introduce peanut products as early as 4 to 6 months. If your baby has an intermediate risk (defined as mild to moderate eczema) the guidelines recommend feeding them peanut products around 6 months. If your baby is low-risk and doesn’t have eczema, you can take a more relaxed approach, introducing peanut products along with other solid foods when you prefer.

The recommendation to introduce peanut products to high-risk babies early was based off one study (the LEAP study), and how exactly to translate those findings is somewhat controversial. Some experts, Dr. Fleischer included, argue that parents shouldn’t stress about introducing peanuts and other allergens so early, noting that some babies won’t be developmentally ready to eat solids at that age. The important thing is to make peanuts and other allergens a regular part of your baby’s diet at least within the first year, Dr. Fleischer said.

Start by introducing a few fruit and vegetable purees, and once your baby has the hang of those, you can try some peanut products, said Dr. Carina Venter, Ph.D., R.D., a registered dietitian specializing in food allergies and an associate professor of pediatrics at University of Colorado Denver School of Medicine. She helped write the government guidelines, including practical and safe recipes for feeding peanuts to babies, since whole or partial nuts are a choking hazard and shouldn’t be offered to kids under age 5. For example, you can mix 2 teaspoons of smooth peanut butter into 2 to 3 teaspoons of hot water (letting it cool before feeding it); or into 2 to 3 tablespoons of fruit or vegetable puree. Start with a small amount of this mixture on the tip of a spoon, and then wait 10 minutes for signs of a reaction. If that’s tolerated, you can offer the rest of the serving.

NIAID guidelines recommend feeding 2 grams of peanut protein (in the form of 2 teaspoons of peanut butter or peanut flour, or 21 pieces of Bamba peanut puffs, for example) about three times per week, as was used in the LEAP study. But Dr. Venter said the most important thing is to keep peanuts as a regular part of the diet. “We don’t want to be anxious about dosing,” she said. “Babies get sick, they don’t want to eat, some days they want to eat lots more, some days they only eat a little bit.” And you want to enjoy feeding your baby, not stress about it, she added.

To introduce other common allergens into your baby’s diet, add foods like yogurt (cow’s milk), Cream of Wheat cereal (wheat) or a variety of nut butters (tree nuts), Dr. Venter recommended. Eggs that are baked (and thus extensively heated) are less likely to cause a reaction than eggs that are lightly cooked, such as when they’re scrambled. So you might try sneaking them into baked goods, such as homemade low-sugar cookies (using fruit puree instead of sugar).

The overall goal is for your baby to have a well-balanced, diverse diet that includes not just potential allergens, but also fruits and vegetables and high iron foods, like slow-cooked meat and iron-fortified baby cereal. Research by Dr. Venter and others has found that babies with a diverse diet are less likely to have food allergies, maybe because this stimulates a more diverse microbiome.

[For more healthy eating tips for your children, see our pieces on food pouches, meal planning, vegetarian diets, instilling healthy eating habits without shame, and dealing with picky eaters.]

A severe allergic reaction, called anaphylaxis, can be life-threatening. These reactions typically affect more than one part of the body (hives plus trouble breathing, for example) and in rare cases can cause a drop in blood pressure. The good news is that research suggests that infants seem to have milder anaphylaxis reactions to food than older kids. Hives and vomiting are the most common symptoms in babies younger than 1, whereas older children are more likely to have respiratory symptoms, like wheezing and difficulty breathing. However, these symptoms can occur at any age and always warrant immediate medical attention.

A mild reaction, like a rash or even a couple of hives, isn’t an emergency, but you’ll still want to let your pediatrician know and follow up with an allergist to figure out whether your child is experiencing an allergy or something else, Dr. Gupta recommended. Rashes can be caused by contact irritation from acidic foods like strawberries or tomatoes, and hives and vomiting can both be caused by infections, for example.

Taking pictures of skin changes and noting the types of foods eaten and the timeline of symptoms can give your allergist clues as to what’s causing the reaction. The doctor might also want to do blood or skin tests, and maybe a food challenge in-office, before making a diagnosis.

Even if you introduce allergenic foods early, your child might still develop allergies. Likewise, “there’s a lot of mothers out there that feel a ton of guilt that something they ate or didn’t eat during pregnancy or breastfeeding may have caused their child’s food allergy, and that is not the case at all,” said Dr. Stukus. “It’s not mom’s fault.”

If your child is diagnosed with a food allergy, he’ll need to completely avoid the food that’s causing it, and will be prescribed an injectable epinephrine pen to use in the case of an anaphylactic reaction. There’s a lot to learn, like how to read labels and cook new recipes, Dr. Venter said. Food allergy websites like Kids With Food Allergies, Snack Safely, FARE and FAACT offer helpful resources.

It’s rare for a child to outgrow a peanut allergy, but many kids can outgrow a milk, egg, wheat or soy allergy by school age, Dr. Keet said, and your allergist will monitor these periodically. Kids with milk and egg allergies can often tolerate these foods in baked goods, so trying them in this form can be a first test and might help kids develop tolerance to these foods.

Research on food allergy treatments like oral immunotherapy (where the child consumes small amounts of the food daily) or epicutaneous therapy (applying small doses of an allergen through a patch) is promising and ongoing. These procedures are being tested on babies as young as 6 to 12 months, with the hope that they’ll be more effective at these younger ages, Dr. Fleisher said. Though there aren’t currently any Food-And-Drug-Administration-approved treatments for food allergy, some allergists offer them, and you may be able to enroll your child in a clinical trial.

Hives, facial swelling, vomiting, wheezing and difficulty breathing are all signs of a serious allergic reaction. If you spot these signs, especially difficulty breathing, get medical help immediately, Dr. Gupta said. It can be hard to tell whether symptoms will go away or get worse, and an anaphylactic reaction can become serious quickly. “When in doubt, be safe and get help,” she said.

Alice Callahan is a health and science journalist, mom of two and the author of “The Science of Mom: A Research-Based Guide to Your Baby’s First Year.”