The guidance parents receive about introducing potential allergens to babies has changed dramatically in the last decade, and many families are working from outdated information. Waiting until a baby is over a year old to introduce peanuts, egg, or fish, which was the advice given to many parents in the 1990s and early 2000s, is now known to increase the likelihood of allergy rather than reduce it.
The research that changed the picture was the LEAP trial, a large UK study that produced results striking enough to change guidance in the UK, USA, Australia, and beyond.
Healthbooq (healthbooq.com) covers weaning and the introduction of solid foods, including practical guidance on allergen introduction in the context of current evidence.
What the LEAP Trial Found
The LEAP (Learning Early About Peanut Allergy) trial, led by Professor Gideon Lack at King's College London and published in the New England Journal of Medicine in 2015, enrolled over 600 high-risk infants (those with severe eczema or existing egg allergy) and randomly assigned them to either consuming peanut products regularly from early infancy or avoiding peanuts entirely until age five.
The results were stark. In the avoidance group, 17 per cent had developed peanut allergy by age five. In the group who ate peanut products, 3.2 per cent had developed allergy. Early consumption reduced the risk of peanut allergy by around 80 per cent. These findings held up in follow-up studies and have been replicated across different populations.
The biological mechanism is related to immune tolerance. When a baby is exposed to a food protein through the gut mucosa, the immune system tends to develop tolerance to it. Exposure through damaged or inflamed skin (as in eczema) may do the opposite, sensitising the immune system. Delayed introduction keeps gut exposure minimal while skin exposure through environmental contact (peanut dust, traces on skin) continues, which may be why delayed introduction increases risk.
Current UK Guidance
The British Society for Allergy and Clinical Immunology (BSACI) guidance, updated following the LEAP trial and subsequent evidence, recommends introducing all the major allergenic foods as part of normal weaning from around six months of age, once the baby has started solids.
This includes peanut products (not whole peanuts, which are a choking hazard, but smooth peanut butter, peanut puffs like Bamba, or thinned peanut paste), egg (well-cooked first, then loosened soft-cooked once tolerated), cow's milk (in cooking and dairy products; not as a main drink until one year), fish, shellfish, sesame, tree nuts (ground or as butter), soya, and wheat.
There is no requirement to introduce them all at once, and no specific order. One new allergenic food at a time, with a gap of a few days before the next, is the practical approach. This allows an allergic reaction to be attributed to the correct food if one occurs.
BSACI guidance is that all babies should have peanut and egg introduced by six to twelve months.
Higher-Risk Babies
Babies with moderate to severe eczema, or who have already had a reaction to one food, are at higher risk of food allergy. For these babies, earlier introduction, between four and six months, is recommended under guidance from an allergy specialist.
A referral to paediatric allergy is appropriate for babies with severe eczema who have not started solids yet, or for babies who have already had an allergic reaction to any food.
Some families with a very strong family history of food allergy seek private allergy testing before introduction, though routine skin prick testing before first introduction is not recommended in babies without risk factors: a negative test is not a guarantee of safety, and a positive test overestimates the chance of clinical reaction.
Practical Introduction
When introducing peanut for the first time at home, small amounts are sensible: half a teaspoon of smooth peanut butter blended into fruit puree is a reasonable starting point. Give it when you will be at home and able to watch the baby for a couple of hours. Most babies tolerate it without any reaction. If the baby is fine, continue including peanut products regularly (the LEAP trial used three times a week).
For a baby who has already had a reaction to a food, or who has severe eczema, introduce in consultation with an allergy team rather than at home.
Signs of an allergic reaction include hives (red raised itchy wheals on the skin), swelling of the lips or eyes, vomiting shortly after the food, a runny nose, and in severe cases, breathing difficulty. Anaphylaxis in infants often presents as pallor, floppy, unusual crying, and breathing changes rather than the classic adult pattern.
If a baby develops any concerning symptoms after a new food, call 999 if there is breathing difficulty or the baby is very unwell. For milder reactions, call 111 or see a GP the same day and do not repeat the food until an allergy assessment has been done.
Key Takeaways
Guidance on introducing allergenic foods to babies changed substantially following the LEAP trial (Learning Early About Peanut Allergy) published in 2015. Earlier avoidance of allergens, which was recommended until the early 2000s, is now understood to increase rather than decrease the risk of allergy. Current guidance from the British Society for Allergy and Clinical Immunology (BSACI) recommends introducing allergenic foods, including peanut products, egg, milk, fish, and sesame, from around six months when weaning begins, alongside other foods. Babies at higher risk (those with moderate to severe eczema or existing food allergy) may benefit from earlier introduction between four and six months with specialist advice. Delaying introduction beyond six to twelve months increases risk.
