Introducing Allergens to Babies: What Changed, and How to Do It Safely

If your parents were told to keep peanuts away from babies until age three, they were following the advice of the time. That advice has been reversed, and the reversal is one of the more consequential changes in infant nutrition guidance in decades.

Current guidance from the National Institute of Allergy and Infectious Diseases and the American Academy of Pediatrics is that early introduction of allergenic foods reduces the risk of developing an allergy, rather than increasing it.

Quick Takeaways

• Delaying allergenic foods does not prevent allergy — early introduction reduces risk
• Peanut and egg should generally be introduced around 6 months, and not before 4 months
• Infants with severe eczema or existing egg allergy are higher risk and should start between 4 and 6 months, after speaking to a doctor
• Whole nuts are a choking hazard at every age in this range — the format matters as much as the timing

What the evidence showed

The landmark LEAP trial compared infants at high risk of peanut allergy who were given peanut-containing foods early against those who avoided it. Early introduction reduced the risk of peanut allergy at age five by roughly 81%, and follow-up work found the protection persisted into adolescence.

That result is the reason guidance changed. Avoidance was not neutral — it appeared to be part of the problem.

When to introduce

Most infants: peanut and egg should be introduced around 6 months of age, but not before 4 months, and once the baby is developmentally ready for solids and has tolerated a few first foods.

Infants with severe eczema or an existing egg allergy: these babies are considered at higher risk of peanut allergy, and guidance suggests introducing infant-safe peanut foods between 4 and 6 months. Because of the higher risk, this group should be discussed with a paediatrician or allergist first — testing is sometimes recommended before the first exposure.

“Developmentally ready” means the usual solids signals: good head and neck control, sitting with support, showing interest in food, and no longer pushing food out with the tongue.

The nine common allergens

In the US, the major allergens are milk, egg, peanut, tree nuts, soy, wheat, fish, shellfish, and sesame.

Peanut and egg have the strongest evidence behind early introduction. The others are introduced alongside ordinary first foods without a special protocol, though the same practical approach applies.

How to do it safely

One new allergen at a time. Introduce a single allergenic food and wait a few days before adding another, so any reaction has an obvious cause.

Start small. A tiny amount on the first exposure — a quarter teaspoon of thinned peanut butter, a small amount of well-cooked egg.

Morning, at home, when you are not rushed. Not at nursery, not at a restaurant, not in the evening. You want to be able to observe your baby for a couple of hours and be able to act.

Watch for two hours. Most reactions appear within this window.

Then keep it in the diet. This is the part people skip. Introduction is not a one-off test — the protective effect comes from ongoing regular exposure, ideally a few times a week. A food introduced once and then dropped for two months has not really been introduced.

Safe formats — the choking issue

Timing and format are separate safety questions, and both matter.

Never give whole nuts or large blobs of thick nut butter to a baby or toddler. Whole nuts are a serious choking hazard into the school years. Thick nut butter can also form a plug.

Safe formats:

• Peanut: smooth peanut butter thinned with warm water, breast milk or formula to a runny consistency; peanut butter stirred into puree or yoghurt; dissolvable peanut puff snacks softened if needed.
• Egg: well-cooked and mashed — hard-boiled, scrambled until firm, or baked into a food. Never runny or raw.
• Milk: yoghurt and cheese are appropriate as foods from around 6 months. Cow’s milk as a main drink waits until 12 months.
• Tree nuts: smooth nut butters thinned, or finely ground nuts mixed into food. Never whole.
• Fish and shellfish: well-cooked, flaked, all bones removed.

What a reaction looks like

Mild to moderate signs, usually within two hours:

• Hives, or a new raised red rash
• Swelling around the lips, face, or eyes
• Vomiting
• Diarrhoea
• Sudden runny nose or sneezing without other illness

Stop the food, and contact your paediatrician before trying it again.

Signs of a severe reaction — call emergency services immediately:

• Difficulty breathing, wheezing, or noisy breathing
• Swelling of the tongue or throat, or a change in the sound of the cry or voice
• Persistent coughing or choking
• Pale, floppy, or unresponsive
• Widespread hives with vomiting

Do not drive to hospital yourself if you see these. Call for an ambulance.

Common questions

Do I need allergy testing first? Not for most babies. For an infant with severe eczema or a known egg allergy, testing before peanut introduction is sometimes recommended — this is a conversation with your paediatrician or an allergist.

What about a family history of allergy? A family history raises the risk somewhat but does not change the general advice. Early introduction is still recommended. Mention it to your paediatrician.

Does eczema mean my baby will have allergies? No, but severe eczema is associated with higher risk, which is why the guidance treats that group separately.

Can I introduce allergens if my baby is exclusively breastfed? Yes — the guidance is about introducing solid foods and applies regardless of milk feeding.

Is baby-led weaning compatible with this? Yes. The formats above work within a baby-led approach; see our baby-led weaning guide for the wider method.

The short version

Introduce peanut and egg around 6 months, not before 4 months, in a safe format, one at a time, in the morning at home — then keep them in the diet regularly. Speak to your paediatrician first if your baby has severe eczema or a known egg allergy.

The instinct to protect a baby by keeping risky foods away is a good instinct pointed in the wrong direction here. On this specific question, the cautious-feeling choice turned out to be the riskier one.

Related reading

For the wider picture on starting solids, see our baby-led weaning guide, and iron-rich foods for toddlers for the nutrient that most often needs attention once solids are established. If feeding is a struggle more generally, picky eater toddler tips may help.

This article is general information based on published NIAID and AAP guidance and does not replace medical advice. Talk to your paediatrician before introducing allergens, particularly if your baby has severe eczema, an existing food allergy, or a strong family history.