For a generation, the advice was to wait: hold off on peanut, egg, and other common allergens until your baby was older, the thinking being that a less-mature system was safer kept away from risky foods. It made intuitive sense. It was also, it turns out, backwards.
The research flipped. We now know that for most babies, introducing allergens early and keeping them in the diet helps prevent food allergies — and that delaying may do the opposite. If you've been nervously eyeing the peanut butter, here's what changed, and exactly how to introduce the scary foods safely.
The science that flipped: the LEAP study
The turning point was a landmark trial called LEAP — Learning Early About Peanut Allergy. Researchers took babies at high risk of peanut allergy and split them into two groups: one regularly ate peanut from infancy, the other avoided it. The results were dramatic enough to rewrite the guidelines.
As the American Academy of Pediatrics summarizes the data: "At 5 years, only 3 percent of the kids who ate peanut products were allergic to them — compared with 17 percent of those who didn't eat peanuts." In other words, early, regular exposure slashed the rate of peanut allergy. Avoidance — the old advice — was associated with more allergy, not less.
This led to the Addendum Guidelines for the Prevention of Peanut Allergy from the National Institute of Allergy and Infectious Diseases (NIAID), which formalized early introduction by risk group. The leading theory for why this works: a baby's immune system learns tolerance through the gut. Meet a food early and regularly by mouth, and the body is more likely to file it under "food" rather than "threat."
When to start: around 6 months for most babies
For the typical baby, the timing lines up with starting solids in general. The AAP advises that once "your baby tolerates a few first foods, and there is no reason to think they are at increased food allergy risk, you can start to introduce the more highly allergenic foods." In practice that's usually around 6 months, after your baby is handling a handful of simpler foods.
Critically, there's no reason to introduce allergens in any particular order, or to save them for last. Egg, peanut, dairy, wheat, soy, fish, shellfish, tree nuts, and sesame can join the rotation right alongside sweet potato and oatmeal. The old practice of methodically delaying the "dangerous" foods is exactly what the evidence overturned. The CDC likewise notes that potentially allergenic foods can be introduced when other solid foods are introduced.
A practical habit worth keeping: introduce new foods one at a time, with a day or so in between, so that if a reaction happens you know the culprit. Offer allergens at home, earlier in the day, when you can keep an eye on your baby for a couple of hours afterward — not right before bed or on the road.
Safe textures: no whole nuts, ever
Early introduction does not mean handing a baby a peanut. Whole nuts and globs of thick nut butter are serious choking hazards. The AAP is explicit: "Do not feed whole peanuts or tree nuts to babies or young children — they are choking hazards." The CDC's choking-hazard guidance lists nuts and seeds among foods to avoid for young children for the same reason.
The goal is the protein in a baby-safe form. Easy ways to do it:
- Peanut: Thin a small amount of smooth peanut butter into warm water, breast milk, formula, pureed fruit, yogurt, or cereal until it's a loose, lump-free consistency. The AAP describes mixing and thinning "a small amount of peanut butter in cereal, pureed fruit or yogurt." Dissolvable peanut puffs designed for infants are another simple option. Never thick spoonfuls, never whole or chopped nuts.
- Egg: Well-cooked and mashed — scrambled until firm, or hard-boiled and mashed (often with a little breast milk, formula, or water).
- Other allergens: Smooth, age-appropriate textures — yogurt or a sliver of cheese for dairy, well-cooked flaked fish (bones removed), smooth tahini thinned out for sesame.
If you're doing finger foods rather than purees, the same texture logic applies. Our guides to starting solids: when and how and baby-led weaning vs. purees cover safe sizing and gagging-versus-choking in more depth.
High-risk babies: talk to the doctor first
Most babies can start allergens at home around 6 months without any special steps. But some need a conversation first. A baby is considered high risk for peanut allergy if they have severe, persistent eczema (the kind needing frequent prescription treatment) and/or a known egg allergy.
For these babies, the AAP is clear: "You should talk with your child's pediatrician first." The NIAID-based guidelines may recommend allergy testing before introduction, and — if the green light is given — introducing peanut as early as 4 to 6 months, sometimes with the first taste supervised in a medical setting. As the AAP explains, for high-risk infants "testing for peanut allergy and introduction of peanut-containing foods under supervision of a health care provider is a consideration."
So the rule of thumb: mild or no eczema and no known food allergy → introduce at home around 6 months, no testing needed. Severe eczema and/or egg allergy → loop in your pediatrician or an allergist before you start. When in doubt, ask — a quick check-in at the 2-to-4-month visit is a great time to raise it.
Keep them in the diet
Here's the step that's easiest to forget: introduction is not a one-and-done. The protection comes from ongoing, regular exposure, not a single heroic taste. A baby who tries peanut once and never sees it again doesn't get the benefit the LEAP study found.
So once your baby tolerates an allergen, keep it in the rotation. The AAP advises keeping allergens "in their diet routinely in developmentally appropriate portions" — for peanut, that's on the order of a couple of teaspoons of peanut butter a few times a week. Make these foods a normal, recurring part of meals rather than a rare event.
What a reaction looks like
Most first tastes go fine, and most reactions are mild — but knowing the signs lets you act calmly. Watch in the couple of hours after a new allergen for hives or widespread redness, swelling of the lips or face, vomiting, coughing or wheezing, trouble breathing, or unusual fussiness or floppiness.
Mild signs (a few hives, some redness around the mouth) warrant a call to your pediatrician. But call 911 right away for any trouble breathing, swelling of the face or throat, repeated vomiting, or a baby who goes pale and limp — these can signal a severe reaction. This is precisely why you introduce allergens one at a time, at home, during the day: it turns a scary unknown into something you can see early and handle. For a fuller picture, see our guide to food allergies in babies and toddlers.
The bottom line
The advice genuinely reversed, and it's worth internalizing: for most babies, introducing peanut, egg, and other allergens early — around 6 months, once a few foods are tolerated — and keeping them in the diet is a powerful, evidence-based way to prevent food allergies. Skip whole nuts and thick butters in favor of thinned, smooth, baby-safe textures. If your baby has severe eczema or a known egg allergy, talk to the doctor before you start. Then offer the food, watch your baby, and — if all goes well — keep it coming. Early and often beats late and never.
This article is educational and not medical advice. Always check with your pediatrician/provider.