If you have any older relatives offering weaning advice, you may already be hearing the old rule — wait until the baby is at least one before peanut, two before egg, three before fish. That advice was given to a generation of parents in good faith, and it turned out to be exactly the wrong way round. Delaying allergens is now understood to increase the chance of allergy, not reduce it.
The change came from a single landmark trial — the LEAP study at King's College London — and the results were striking enough that paediatric allergy guidance in the UK, US, Australia, and across Europe was rewritten within a few years.
Healthbooq (healthbooq.com) covers weaning and the introduction of solid foods, including practical guidance on allergens.
What the LEAP Trial Actually Showed
The LEAP (Learning Early About Peanut Allergy) trial, published in the New England Journal of Medicine in 2015, recruited more than 600 high-risk infants — babies with severe eczema or an existing egg allergy. Half were asked to eat peanut products regularly from infancy. The other half were asked to avoid peanut entirely until age five.
By age five:
- 17% of the avoidance group had developed peanut allergy.
- 3.2% of the early-eaters had.
That is around an 80% reduction in allergy risk, in the babies who were already at the highest risk. Follow-up studies have shown the protection persists once the children stopped eating peanut regularly, and the same pattern has been replicated for egg.
The biology behind it makes sense. The immune system seems to learn tolerance through the gut — a baby's first introduction to a food protein via swallowing usually teaches the immune system that this protein is food, not an enemy. The same protein meeting the immune system through cracked, eczema-inflamed skin (think peanut dust on a kitchen counter or on a parent's hands) gets read as an invader. Delaying introduction does not stop skin exposure. It just removes the gut exposure that builds tolerance.
The Current UK Guidance
The British Society for Allergy and Clinical Immunology (BSACI) now recommends introducing all of the major allergenic foods as part of normal weaning from around six months, alongside everything else.
The major allergens to get in:
- Peanut — smooth peanut butter thinned with water or stirred into yoghurt, peanut puffs (Bamba is the brand most parents reach for). Never whole peanuts or chunks of nut butter — both are a choking risk under five.
- Egg — well-cooked first (hard-boiled, scrambled solid, in baked goods). Once tolerated, you can move to softer-cooked.
- Cow's milk — in cooking, in dairy, on cereal. Not as a main drink until twelve months.
- Fish and shellfish — flaked into something soft.
- Sesame — tahini stirred into yoghurt or hummus.
- Tree nuts — ground or as smooth nut butters.
- Soya and wheat — usually slip in via normal foods anyway.
There is no required order, and no need to introduce them all on the same day. The practical approach is one new allergenic food at a time, with a couple of days before the next, so that if a reaction does happen you know which food caused it. By twelve months, peanut and egg should both be in the regular diet and staying there — irregular exposure is not the same as no exposure, but the LEAP follow-up suggested keeping them in the diet at least a couple of times a week through toddlerhood.
Babies Who Need a Different Plan
Two groups of babies do not just go ahead at home:
- Babies with moderate or severe eczema (especially anyone needing daily steroid creams).
- Babies who have already had a reaction to a food.
Both should be introduced to allergens earlier than six months — usually between four and six — and ideally after a paediatric allergy assessment. If your baby has severe eczema and has not started solids yet, ask your GP for an allergy referral now rather than after a reaction.
A note on testing: skin-prick tests and blood IgE tests before any introduction are not routinely recommended in babies without risk factors. False positives are very common in this age group, and a positive test in a baby who has never eaten the food does not reliably predict a real-world reaction. The right time for testing is when there is something specific to test for — a reaction, severe eczema, or a strong family pattern of confirmed food allergy.
Doing It at Home
A practical first peanut introduction looks like this:
- Pick a calm morning when you will be home for a couple of hours.
- Stir half a teaspoon of smooth peanut butter into a few spoonfuls of warm fruit purée or yoghurt until it is fully blended.
- Offer it. If they tolerate it, gradually build up over the next few days.
- Once it is going down without issue, aim to keep peanut in the diet two or three times a week — that is roughly what the LEAP babies were doing.
Most babies will eat it without any reaction at all. The point of doing it at home, in the morning, is not because a reaction is likely — it is so that if one does happen, you have time and daylight to deal with it.
What a Reaction Looks Like
The signs to watch for in the next two hours:
- Hives — raised, red, itchy patches on the skin, sometimes spreading.
- Swelling around the lips, eyes, or face.
- Vomiting that comes on shortly after the food.
- Sudden runny nose, sneezing, or a hoarse cry.
- In severe reactions: noisy or laboured breathing, persistent cough, going pale and floppy, or unusual drowsiness.
Anaphylaxis in babies does not always look like the textbook adult version. Pallor, sudden floppiness, an unusual cry, and breathing changes after a food can all be the first signs — those alone are enough to call 999.
For mild skin-only reactions (a few hives that fade, no other symptoms), call 111 or your GP the same day, and do not give that food again until your baby has been seen by an allergy team. For anything involving breathing, swallowing, or unusual drowsiness — 999 first, questions later.
Key Takeaways
Old advice to avoid peanut, egg, and fish in the first year was wrong — it actually raises allergy risk. Current UK guidance (BSACI) is to introduce all the major allergens during normal weaning from around six months, and to have peanut and egg in the diet by twelve months. Babies with moderate-to-severe eczema or an existing food allergy need earlier introduction (4–6 months) and a paediatric allergy referral first.
