Food And Allergy Prevention: The Advice Has Reversed

A reader asks Dr Lee if there are any food that can prevent allergies.

This page’s topic is one of the rare places where standard parenting advice has performed a full U-turn, and where following the old version actively causes the thing it tried to prevent.

For years, parents were told to delay the scary foods: no peanut before three, hold the egg, keep shellfish far from the highchair. Then researchers tested it. The landmark LEAP trial in 2015 found that introducing peanut early slashed peanut allergy rates in high-risk babies. A decade on, the real-world data has followed: US figures published in 2025 show peanut allergy in under-threes down by more than 40% since guidelines flipped to early introduction. Delay, was the risk factor.

What the current guidance says.

Introduce allergenic foods early: from around six months, alongside other solids (not before four months), including peanut, egg, fish, wheat, soy and dairy in age-safe forms.
Don’t deliberately delay any of them. Waiting doesn’t protect; sustained early exposure appears to teach the immune system tolerance.
One group needs a doctor first: babies with severe eczema or an existing food allergy are the high-risk group. Introduce allergens for them with medical guidance, sometimes after testing. That’s the one carve-out, and it’s important.

How to do it

Age-safe forms only. Whole nuts are a choking hazard until five. Peanut means smooth peanut butter thinned into porridge or puree, or peanut powder stirred through. Egg means well-cooked egg (the strip of omelette, the hard-boiled mash), not raw or runny at this age.
One new allergen at a time, early in the day. Not because disaster is likely, it isn’t, but so that if a reaction happens, you can see it, name the culprit, and you aren’t watching hives appear at midnight.
Start small, then keep it coming. A taste the first time, building to regular portions. The protective effect in the research came from sustained exposure, a few times a week, not a single ceremonial introduction. The peanut butter that appears once and vanishes for a month isn’t the protocol.
Keep the eczema managed alongside. Well-controlled skin seems to count in its own right, and a baby with significant eczema is exactly the one whose allergen plan should go through the doctor.

What a reaction looks like and what to do

Mild and most common: a few hives around the mouth, redness, perhaps a vomit. Settle, note the food, and discuss with your doctor before the next exposure.

Emergency, call 995: any breathing difficulty, wheeze or persistent cough after eating; swelling of tongue or throat; widespread hives with floppiness, paleness or vomiting; or collapse. Severe first reactions in young babies are rare, but the response is an ambulance, not a wait-and-see.

For calibration: reactions at first introduction are uncommon, mild ones vastly outnumber severe ones, and fear of this moment is precisely what drove the delay advice that made allergies more common. The reaction plan exists so you can proceed confidently, not so you don’t proceed.

Corrections to the old advice

“Delay allergens to prevent allergy”: reversed. Early, sustained introduction is the protective strategy; deliberate delay is associated with more allergy, not less.
“Mums should avoid peanuts in pregnancy and breastfeeding to protect the baby”: also retired. There’s no good evidence that maternal avoidance prevents allergy in the child, and mothers gave up satay for nothing. (Any change for a mother’s own allergy is a different question, hers to manage with her doctor.)
“No food can prevent allergy”: half-true, in an unexpected direction. No superfood prevents allergy; but the allergens themselves, arriving early and often, are the closest thing to prevention the evidence has produced.

Frequently asked questions

When should I introduce peanut and egg to my baby?

From around six months, with other solids, not before four months, in age-safe forms: thinned smooth peanut butter or peanut powder, and well-cooked egg. For babies with severe eczema or an existing food allergy, plan it with your doctor first.

Does delaying allergens protect my baby?

No, that advice has been reversed. Trials and a decade of real-world data point the same way: early, sustained introduction reduces allergy; delay is associated with more of it.

How often should allergens appear once introduced?

Regularly: think a few times a week in normal portions. The protection in the research came from sustained exposure, not one-off tastings.

What if my baby has eczema?

Mild eczema: proceed, keeping the skin well managed. Severe eczema, or an existing food allergy, is the high-risk group. Allergen introduction for these babies goes through your doctor, sometimes with testing first.

What does an allergic reaction look like in a baby?

Usually mild: hives near the mouth, redness, a vomit, which you note and raise with your doctor. Breathing difficulty, tongue or throat swelling, widespread hives with floppiness, or collapse are 995 territory immediately.

Should I avoid peanuts while pregnant or breastfeeding?

Not for allergy-prevention purposes. Maternal avoidance has no good evidence behind it and is no longer advised. Eat the satay.

What to remember

The advice flipped: allergens go in early, around six months, age-safe forms, one at a time, then regularly, and nothing is deliberately delayed. The one exception that goes through a doctor first: severe eczema or an existing allergy.

Know the mild-versus-emergency distinction, and proceed anyway. The fear that kept peanut out of highchairs is what filled the allergy clinics.