When to Introduce Peanut and Other Allergens: What the LEAP Study Found
By Lybadora Editorial Team3 min read
US guidelines, built on the LEAP trial, sort infants into three groups. Infants with no eczema or egg allergy can have peanut foods introduced along with other solids, on the family's own timeline. Infants with mild-to-moderate eczema should have peanut foods introduced at around 6 months. Infants with severe eczema and/or an egg allergy are considered high-risk, and guidelines suggest introducing peanut foods as early as 4 to 6 months, ideally after allergy testing. In the original LEAP trial, early introduction produced an 81% relative reduction in peanut allergy by age 5 compared with avoidance.
Explanation
For years, the standard advice ran the opposite direction: delay peanut. The LEAP trial is the reason that changed, and it changed because the trial measured an outcome directly rather than reasoning about risk in the abstract.
Supporting evidence
The Learning Early About Peanut Allergy (LEAP) trial enrolled infants at high risk of peanut allergy (because of severe eczema and/or egg allergy) between 4 and 11 months old, and randomised them to either regular peanut consumption or avoidance until age 5.
| Outcome | Result |
|---|---|
| Peanut allergy at age 5, early-consumption group vs. avoidance group | 81% relative reduction |
A follow-up study, LEAP-On, then asked a harder question: does the protection last if peanut is stopped? Around 550 of the original participants avoided peanut for a further 12 months, regardless of which group they had started in, and were then tested again at age 6.
| Outcome after 12 months of avoidance | Result |
|---|---|
| Allergic, original early-consumption group | 4.8% |
| Allergic, original avoidance group | 18.6% |
NIH: Providing lasting protection from peanut allergy · LEAP-On, NEJM 2016
Following the trial, NIAID published addendum guidelines in 2017 sorting infants into three risk tiers:
| Risk group | Guidance |
|---|---|
| No eczema or egg allergy | Introduce peanut foods with other solids, per family preference |
| Mild-to-moderate eczema | Introduce peanut foods at around 6 months |
| Severe eczema and/or egg allergy | Consider allergy testing first; introduce as early as 4–6 months if appropriate |
What the numbers mean
The LEAP-On result is the more surprising of the two findings, because it separates two different questions that are easy to conflate: does early exposure prevent allergy, and does the body need continuous exposure to stay protected? The 4.8% versus 18.6% split, measured after both groups had avoided peanut equally for a year, shows the protection from early introduction held without ongoing consumption, it was not simply postponing the same outcome.
The three-tier structure exists because risk is not the same for every infant, and the guidance treats "when" as inseparable from "how risky is a first exposure." A high-risk infant is the one group where testing before introduction is specifically suggested, the timeline is earlier for that group precisely because the stakes of an untested first exposure are higher.
What parents can observe
- Eczema severity and any known egg allergy, since that is what places an infant in the high-risk tier where testing is suggested.
- How and when peanut was first introduced, recorded rather than recalled, particularly useful if a reaction ever needs to be discussed with a clinician.
- Any reaction at first exposure, treated as an immediate medical question rather than something to watch over subsequent days.
What may explain a pattern
There is no "pattern" to watch for with allergen introduction the way there is with sleep or feeding volume, a reaction, if one happens, happens at or shortly after exposure, not as a trend across days. That is part of why the guidance for high-risk infants specifically suggests testing and, often, an in-office first exposure rather than an at-home one.
What parents can do
Talk to a paediatrician about which risk tier applies before introducing peanut, particularly if there is eczema or an egg allergy in the picture. For lower-risk infants, the guidance is permissive rather than prescriptive about exact timing, introduce peanut foods alongside other solids rather than delaying them, which is the opposite of what guidance said a decade ago.
Safety considerations
Introducing peanut and other allergens to a high-risk infant, one with severe eczema, an egg allergy, or a prior reaction, should be discussed with a paediatrician or allergist first, and guidelines suggest allergy testing before the first exposure in that group. The first introduction of any new allergen should follow current safe-introduction practices (a small amount, at home, when the baby is well) and any signs of an allergic reaction should be treated as a medical concern, not a pattern to observe over time. This article describes population-level research findings, not guidance for an individual child with a known allergy or reaction history.