If, like me, you’re a parent of a young child, there’s one thing you’ve come to fear above all else. (And no, it’s not “Golden” from KPop Demon Hunters played for the 10,000th time, though that’s a close second.)

It’s the humble peanut. Even if your child isn’t allergic to the nuts, past surveys have shown as many as 4.5 percent of kids in the US are, which means consistently scouring lunchboxes and snack packs for even traces of peanuts. And for a long time, this problem was getting worse — the self-reported prevalence of peanut or tree nut allergies among children in the US more than tripled between 1997 and 2008.

So here’s a rare public health win you can feel at the playground: Researchers at Children’s Hospital of Philadelphia (CHOP) compared peanut and food allergies before pediatric guidelines about feeding changed in 2017 and after, and found that infants and toddlers are being diagnosed with far fewer food allergies now. Comparing pre-guideline rates with the post-2017 period, diagnoses of any food allergy were about 36 percent lower — driven largely by a roughly 43 percent drop in peanut allergy.

The sharp reduction in peanut allergies doesn’t just make it easier for parents to pack lunches across the country. It represents “prevention of a potentially deadly, life-changing diagnosis,” Dr. Edith Bracho-Sanchez, a pediatrician at Columbia University Irving Medical Center, told the New York Times. And it happened because public health researchers looked hard at the science, realized what they were doing to prevent allergies wasn’t working — and changed tack.

What changed — and why it worked

For years, well-meaning medical advice told parents that the way to protect children from developing food allergies was to delay the introduction of allergenic foods. In 2000, the American Academy of Pediatrics (AAP) laid out the following timetable for parents: delay introduction of cow’s milk until an infant is 1 year old, eggs until 2 years old, and nuts and fish until age 3.

Infant immune and gut systems are still immature, so waiting until children were older and those systems had more fully developed to introduce potentially allergenic foods seemed to make sense, and the advice was widely adopted by parents.

But that reasoning began to unravel in 2015 with the LEAP trial, a gold-standard randomized trial that found that high-risk babies who started peanuts early and kept eating it through childhood had about an 80 percent lower risk of developing a peanut allergy by age 5, compared to those kept off the nuts. Follow-up work showed that protection persisted into adolescence.

The shift reveals the value of dual-exposure: Early oral exposure to allergenic proteins found in foods like peanuts trains the immune system to tolerate them, while exposure through inflamed skin — common in babies with eczema — primes sensitization. So the new guidelines pushed safe oral introduction in the first half-year in forms infants can handle, like thinned peanut butter or puffs as opposed to whole nuts.

What followed was evidence-driven public health at its best. The data was strong enough to trigger a policy 180: A 2017 addendum to the guidelines urged parents to introduce peanuts between 4 and 6 months. A 2021 consensus document from allergists and immunologists went further, also recommending the introduction of egg and other allergens at the same age. It’s one of those rare times when the science was clear, the guidance became clear, and the desired outcomes followed, as the new study from CHOP demonstrated.

The new data on food allergies

The CHOP team mined AAP-affiliated electronic health records to compare results from before and after the updated guidelines. Peanut allergy diagnoses fell from 0.79 percent to 0.45 percent among infants and toddlers, while any IgE-mediated food allergy — an immune reaction to specific food proteins that triggers the release of immunoglobulin E (IgE) antibodies, which is what drives allergy symptoms — fell from 1.46 percent to 0.93 percent. Notably, peanuts even dropped from the most common allergy culprit to number two, with egg moving to first — exactly what you’d expect given that the AAP’s intervention was initially peanut-specific.

The researchers estimate the shift has already prevented tens of thousands of cases — on the order of around 40,000 peanut allergies, and some 60,000 food allergies overall — since 2015. That’s a huge payoff for what boils down to something as simple and cheap as giving your 5-month-old the occasional peanut.

And there are likely even more gains to be realized, because the adoption of the new allergy guidance has been real but incomplete: Only about 29 percent of pediatricians reported fully implementing the 2017 recommendations a couple of years in, with somewhat higher compliance from allergists. The fact we still saw such sharp declines in allergies suggests the effects could be even bigger as awareness spreads among doctors and parents alike.

It’s more than peanuts

Peanut allergies are no joke. They tend to persist for life, they drive a disproportionate share of all severe allergic reactions, and dealing with them reshapes daily life in everything from school parties to air travel. Preventing even a slice of new cases means fewer EpiPens in backpacks, fewer late-night ER runs, and less of the background anxiety that families of allergic kids know too well. And there’s a real economic dividend: Estimates put the annual US economic burden of childhood food allergies at around $25 billion, or around $4,000 per affected child per year. Prevent those allergies from ever developing in the first place, and you lighten that load for years.

But there’s a broader lesson for health here that goes well beyond allergies. When a large, decisive trial shows an actionable prevention behavior, change the guidance decisively, say it simply, and measure outcomes in the real world. Then close the implementation gap with better clinician prompts, clearer parent handouts, and practical tips for high-risk families.

Scientific expertise is under threat as never before — and some of that criticism is warranted. But If you’re looking for evidence that public health can change its mind in the face of countervailing evidence, here it is, delivered in baby-safe spoonfuls.

A version of this story originally appeared in the Good News newsletter. Sign up here!

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