Allergens 101
How to safely introduce peanuts, eggs, and the other top allergens
Allergen introduction is one of the topics that worries parents the most — and it's also one where the science has shifted significantly in the last decade. The short version: introducing allergens early is now considered protective, not risky. Here's what you need to know to do it safely and confidently.
Why early introduction matters
Research — including the landmark LEAP (Learning Early About Peanut Allergy) study — showed that introducing peanuts early and regularly actually reduces the risk of developing a peanut allergy by up to 80% in high-risk infants. Based on this and similar evidence, major health bodies now recommend introducing the top allergens from around 6 months of age, rather than avoiding them. Waiting until later, once thought to be the safe approach, is no longer advised for most babies.
The top allergens to introduce
The nine major food allergens are: cow's milk, eggs, peanuts, tree nuts, wheat, soy, sesame, fish, and shellfish. These account for the vast majority of allergic reactions in children. You don't need to introduce all of them in the first week, but none of them should be intentionally delayed beyond the first few months of weaning. Introduce them one at a time so you can identify the cause if a reaction does occur.
How to introduce them safely
For peanuts, use smooth peanut butter (never whole nuts, which are a choking hazard) thinned to a very runny consistency with a little cooled boiled water or breast milk. Offer a small amount — about a quarter teaspoon — mixed into a puree your baby already tolerates. For egg, ensure it is always well-cooked (scrambled or hard-boiled), as raw or undercooked egg carries bacterial risk. For cow's milk, full-fat dairy like yogurt or cheese can be offered as food from 6 months, though cow's milk as a drink should wait until 12 months.
The one-at-a-time rule
When introducing any new allergen, offer it on its own or mixed into a food your baby has already eaten safely. Don't introduce two new allergens on the same day. Give each new allergen in the morning so you have the rest of the day to observe your baby — and so you're not trying to monitor anything overnight. Keep offering the same allergen over a few days to build tolerance, rather than offering it just once.
Signs of an allergic reaction
Most allergic reactions in babies are mild and involve hives, a rash around the mouth, or mild swelling. More serious reactions — anaphylaxis — are rare but can include sudden swelling of the lips or tongue, difficulty breathing, loss of colour, or becoming very floppy. If you see any of these severe signs, call 999 (UK) or 911 (US) immediately. For mild reactions, contact your GP or healthcare provider for guidance on next steps.
A note on high-risk babies
If your baby has severe eczema or has already had a food allergic reaction, speak to your GP or an allergist before introducing peanuts or other top allergens at home. They may recommend a supervised introduction in a clinical setting. For most babies without these risk factors, allergen introduction at home is safe and encouraged.
Key takeaways
Scientific sources
The guidance in this guide is based on these references.