Introducing Allergens: Why Early Is Now Better Than Late

Few pieces of feeding advice have reversed as completely as the guidance on allergens. A decade ago, parents were told to delay peanuts, eggs, and other common allergens to prevent allergies. The evidence now says the opposite: early, deliberate introduction of allergenic foods, around four to six months, is one of the most effective ways to prevent food allergies. The turnaround is one of the clearest in modern pediatrics.

What the LEAP trial changed

The shift was driven largely by the LEAP (Learning Early About Peanut Allergy) trial, a landmark study that found early peanut introduction reduced peanut allergy by roughly 80 percent in high-risk infants. The findings were strong enough to change global guidelines almost overnight. The mechanism appears to be that early, controlled exposure teaches the immune system to tolerate the protein rather than react to it.

Waiting does not protect a baby from allergies. For most children the opposite is true: early introduction is the prevention.

How to introduce allergens

The current guidance is to introduce common allergens (peanut, egg, dairy, wheat, tree nuts, fish, soy, and sesame) one at a time, starting around four to six months, in age-appropriate forms. Peanut, for example, is introduced as thinned peanut butter or a peanut-containing powder, never whole nuts or chunks. The key is early, regular, ongoing exposure: introducing once is not enough; keeping the food in the diet regularly is what maintains tolerance.

• Introduce common allergens one at a time from around 4–6 months.
• Use age-appropriate forms, thinned peanut butter, never whole nuts.
• Keep the food in the diet regularly; a single exposure is not enough.
• For high-risk infants (severe eczema or existing allergy), talk to your provider first.
• Watch for reactions, but know that severe reactions on first exposure are uncommon.

The high-risk exception

There is one important exception: infants with severe eczema or an existing food allergy are at higher risk, and for these children the guidance is to consult a provider before introducing allergens, sometimes with testing first. For the large majority of infants, however, the message is simple: do not delay. Early, regular introduction is the prevention.

Keeping the food in the diet

The part of the new guidance that most families miss is the maintenance, not the early start. The LEAP trial's protection came from regular, ongoing exposure, not a single taste. A peanut introduced at five months and then dropped for months offers little protection; the immune system needs to keep seeing the protein to keep tolerating it. The practical rule that falls out of this is simple: once an allergen is introduced and tolerated, keep it in regular rotation.

This is also the part that makes the early introduction approach forgiving. You do not need to orchestrate a perfect schedule of allergens; you need to fold the common ones into ordinary family meals and keep them there. A smear of thinned peanut butter a few times a week, an egg scrambled into breakfast now and then, a little yogurt, these small, repeated exposures are exactly what the evidence supports, and they fit into a life that already has enough to manage.

• Protection comes from regular exposure, not a single introduction.
• Once an allergen is tolerated, keep it in rotation, don't let it lapse.
• Fold allergens into family meals rather than staging special 'allergen days.'
• Two to three exposures a week per allergen is a reasonable, low-stress rhythm.

The reversal can be jarring for parents who heard the old advice, but the evidence is unusually strong. If you are anxious about introducing allergens, a quick conversation with your pediatrician can tailor the plan to your child. For most families, though, the takeaway is reassuringly simple: offer the common allergens early, keep them in the rotation, and let the immune system do what it is built to do.