When should babies try peanut? The trial that flipped the advice

For babies at high risk of peanut allergy — those with severe eczema, egg allergy, or both — the strong evidence now points the opposite way to the advice of a generation ago: introduce peanut early, in the first year of life, rather than avoid it. The landmark LEAP randomised trial showed that early, sustained peanut consumption sharply reduced peanut allergy by age five [s1], and a follow-up study showed the protection largely persisted even after a year off peanut [s2]. The instinct to delay allergenic foods, for these infants, turned out to be backwards.

What LEAP did

LEAP (Learning Early About Peanut Allergy) randomly assigned 640 infants, aged at least 4 months but younger than 11 months and all at high risk — with severe eczema, egg allergy, or both — to either consume or avoid peanut until 60 months of age [s1]. The children were split into two groups by a baseline skin-prick test: one with no measurable reaction to peanut, and a smaller one already showing mild sensitisation [s1].

The results were large. Among the 530 infants who started with a negative skin-prick test, the prevalence of peanut allergy at 60 months was 13.7% in the avoidance group and 1.9% in the consumption group (P<0.001) [s1]. Among the 98 who were already mildly sensitised, allergy developed in 35.3% of avoiders versus 10.6% of consumers (P=0.004) — a benefit even among those whose immune systems had begun to react [s1]. There was no significant difference between the groups in serious adverse events [s1].

Did the protection last?

A fair worry is that early eating simply delays allergy rather than preventing it. The follow-up trial, LEAP-On, tested that by asking all children to avoid peanut entirely for the next 12 months [s2]. Of 556 who continued, peanut allergy at 72 months was 18.6% in the original avoidance group versus 4.8% in the original consumption group (P<0.001) [s2]. Crucially, stopping peanut for a year did not undo the benefit: allergy in the consumption group rose only from 3.6% at 60 months to 4.8% at 72 months, a change that was not statistically significant (P=0.25) [s2]. The tolerance built in infancy held.

The catch: high-risk babies should be assessed first

The trial's own design carries the main caution for parents. Infants who were already sensitised had far higher allergy rates, and some children do react to peanut [s1]. For that reason, babies at high risk — those with severe eczema and/or a known egg allergy — should be assessed by a clinician, often with a skin-prick or blood (specific IgE) test, before peanut is first introduced, rather than started at home unsupervised [s1]. For babies without those risk factors, the evidence supports simply including smooth peanut among first foods from around six months, alongside other solids.

One practical point sits underneath all of this: whole peanuts and large blobs of stiff peanut butter are choking hazards for infants and should never be used. Peanut is introduced as a thin smear of smooth peanut butter mixed into food, or as a dissolvable peanut puff — texture matters as much as timing.

It is also worth being precise about what LEAP does and does not prove. It enrolled only high-risk infants — those with severe eczema, egg allergy, or both — so its dramatic numbers apply most directly to that group, the very babies whose parents were once told to be most cautious [s1]. The trial cannot say that a specific low-risk baby will benefit by the same margin, only that early introduction did no harm and prevented a large share of allergy in the children studied, and that avoidance was the strategy that backfired [s1]. That reversal — from "delay to be safe" to "introduce to be safe" — is the single most important thing the trial changed [s1][s2].

How to read this

LEAP reset the default for high-risk infants from avoid to introduce early, and LEAP-On showed the effect was durable [s1][s2]. The nuance is that "early introduction" for a high-risk baby means introduction after assessment, not a leap of faith at the kitchen table [s1].

This guidance is about preventing allergy in babies who are not already known to be allergic. A child with a diagnosed peanut allergy is a different situation entirely and should be managed only by a specialist. Signs of an allergic reaction — hives, facial or lip swelling, vomiting, wheeze, or a floppy, pale child — mean stopping the food and seeking urgent care; suspected anaphylaxis is an emergency. This article is informational and not medical advice.