For much of the 1990s and 2000s, parents were advised to avoid giving peanuts and other common allergenic foods to young babies on the grounds that this would reduce allergy risk. The guidance was logical-sounding but wrong. It was based on immunological theory rather than trial evidence, and when the trial evidence finally arrived, it showed the opposite: early introduction of allergenic foods reduces allergy, avoidance increases it.
The LEAP trial published in 2015 changed guidelines globally. A generation of parental avoidance strategies had contributed to the rise in childhood peanut allergy. Understanding what the evidence now shows – and what it means for weaning – matters for every family starting their baby on solid food.
Healthbooq (healthbooq.com) covers allergen introduction and weaning.
The LEAP Trial and What It Showed
LEAP (Learning Early About Peanut allergy), led by Gideon Lack at King's College London, randomised 640 infants aged 4-11 months who were at high risk of peanut allergy (severe eczema, egg allergy, or both) to either consume peanut regularly or avoid it. At age 5, just 1.9% of children in the consumption group had developed peanut allergy, compared with 13.7% in the avoidance group – a reduction in allergy of 81% in the high-risk group.
This finding reversed decades of dietary guidance. In 2016, NIAID (US National Institute of Allergy and Infectious Diseases) issued revised guidelines recommending early introduction. In 2018, the NHS updated its weaning guidance, and the current NICE guidance and NHS Start4Life materials recommend introducing allergenic foods from the start of weaning, around 6 months.
The mechanism is believed to involve oral tolerance: the immune system, when exposed to a food protein through the gut (where it encounters regulatory immune cells and a tolerogenic environment), is more likely to develop tolerance than allergy. Sensitisation via the skin – through eczema-broken skin exposed to environmental peanut proteins – appears to prime the immune system toward allergy rather than tolerance. This explains why early eczema is a risk factor for peanut allergy.
Which Babies Need a Different Approach
Most babies can and should be offered all allergenic foods as part of normal weaning from around 6 months. They do not need any special preparation, allergy testing, or medical supervision.
Babies with severe eczema (defined as extensive, requiring daily or near-daily use of potent topical steroids) or an existing egg allergy diagnosed by an allergist are at highest risk of peanut allergy and should be assessed by a paediatric allergist before peanut introduction. This is because a small proportion of these babies already have sensitisation to peanut that could cause a reaction on first exposure.
In practice: if a baby has mild-moderate eczema (easily managed with emollient and occasional mild steroid), they can be offered peanut at home from 6 months without specialist input. Only severe eczema or diagnosed egg allergy triggers specialist assessment.
How to Introduce Allergenic Foods
Peanut should be introduced as smooth peanut butter (not whole peanuts, which are a choking hazard) mixed into food, or as peanut puffs designed for infants. Whole nuts should not be given to children under 5.
The recommended approach: introduce one new allergenic food at a time, early in the day, at home, and wait 2-3 days before introducing the next allergenic food. This allows identification of any reaction and ensures the family is at home when the reaction would be most likely to occur.
Allergenic foods to introduce in the first months of weaning include: peanut, cooked egg (well-cooked initially; raw or lightly cooked later), cow's milk in food (cooking, yogurt, cheese – though milk as a main drink before 12 months is not recommended), wheat (bread, pasta), fish, shellfish, sesame, soya, and tree nuts (as smooth paste or ground).
If a Reaction Occurs
Mild reactions (hives, skin flushing, mild swelling around the mouth) can be managed at home with antihistamine and do not necessarily mean the food must be permanently avoided. Severe reactions (throat tightening, difficulty breathing, vomiting, extreme pallor, limpness) are anaphylaxis: use an EpiPen if prescribed, call 999, and do not re-introduce the food without specialist allergy assessment.
A first-time exposure causing a reaction should lead to allergy assessment rather than permanent avoidance decided at home.
Key Takeaways
Evidence from multiple randomised controlled trials, most significantly the LEAP trial (Learning Early About Peanut, Gideon Lack et al., NEJM 2015), has fundamentally changed guidance on allergen introduction in infancy. The previous recommendation to avoid peanuts and other allergenic foods in infancy to prevent allergy has been reversed: early, regular introduction of allergenic foods – including peanut, egg, wheat, fish, and milk – from around 6 months (or as soon as solids are introduced) reduces rather than increases the risk of developing allergy. Babies with severe eczema or existing egg allergy are at highest risk of peanut allergy and may need specialist assessment before introduction; all other babies should be offered allergenic foods as part of a varied diet from the start of weaning.
