This is one of the few areas of paediatric advice that genuinely changed in the last decade. Until the late 2010s, parents were told to delay peanuts, eggs, and other "high-risk" foods until well past the first birthday. The evidence has flipped: early introduction prevents allergy, delay tends to encourage it. Most parents have heard a version of this but aren't sure how to do it in real life. The mechanics matter as much as the principle.
Healthbooq covers weaning and food introduction with up-to-date allergy guidance.
What Changed and Why
The LEAP (Learning Early About Peanut Allergy) trial, published in the New England Journal of Medicine in 2015, randomised babies aged 4 to 11 months who already had severe eczema or egg allergy — exactly the babies historically considered "too high-risk" to expose to peanut — to either regular peanut introduction or strict avoidance.
Result at age 5: 81% reduction in peanut allergy in the early-introduction group. The follow-up LEAP-On trial showed this protection persisted even after children stopped eating peanut for a year.
Subsequent trials (EAT, PETIT, others) have shown similar effects for egg and other allergens. The mechanism appears to be oral tolerance: regular oral exposure to a food protein in early infancy teaches the immune system to ignore it, while exposure through inflamed skin (in eczema) without prior oral exposure can drive sensitisation.
The practical takeaway: delaying allergens does not protect; in many babies it actively increases the risk of developing an allergy.
The 14 Allergens UK Labelling Covers
UK and EU food labels must declare 14 allergens. The ones most commonly implicated in IgE-mediated childhood food allergy:
- Cow's milk (most common in UK infants)
- Egg (second most common)
- Peanut
- Tree nuts (almond, cashew, hazelnut, walnut, pistachio, etc.)
- Sesame
- Wheat
- Fish and shellfish
- Soy
The rest of the 14 — celery, mustard, lupin, molluscs, sulphites — matter for labelling but are uncommon allergens in young children.
Current Guidance: When to Start
NHS, BSACI, and NICE all align:
- Around 6 months, alongside the introduction of solid foods generally
- Wait until your baby shows readiness for solids: sits with support, head and neck control, no longer pushing food out with the tongue
- Don't introduce allergens before 4 months in any baby — the gut and immune system aren't ready
- Don't deliberately delay them beyond 12 months — that's the window where avoidance increases risk
Risk categories:
- Standard risk (no eczema, mild eczema, no known food allergy): introduce all major allergens from around 6 months at home
- Moderate eczema: same approach — from around 6 months at home. The previous "moderate eczema needs caution" framing has softened
- Severe eczema (eczema needing prescription steroids or hospital input) or existing egg allergy: speak to your GP or health visitor before introducing peanut. Some babies in this group are referred for an allergy clinic skin prick test or supervised first peanut feed
- A sibling with severe peanut allergy: not an automatic specialist referral, but worth a GP conversation; many parents in this group choose to introduce in a clinical setting
If you're unsure which category your baby is in, ask your health visitor or GP.
Practical Introduction: How to Actually Do It
The principles are simple and worth following exactly:
1. One new allergen at a time. If a reaction occurs, you need to know which food caused it.
2. Start with a small amount. A teaspoon-sized portion the first time is enough.
3. At home, during the day. Not nursery, not while travelling, not late evening. You want to watch for 2 hours after and have access to medical care if needed.
4. Watch for 2 hours. Most reactions appear within 30 minutes; the 2-hour window covers nearly all immediate reactions.
5. Build up gradually. If the small portion is tolerated, give a bigger portion the next day, and another the day after. Daily exposure for the first week, then aim for 2 to 3 times a week ongoing.
6. Keep going. Tolerance requires regular exposure. If you stop feeding peanut for several months after the initial introduction, the tolerance can fade. The current advice is to include each tolerated allergen at least weekly through the first few years.
How to Give Each Allergen Practically
Peanut.- Smooth peanut butter — never whole peanuts (choking hazard until at least 5 years)
- Mix a small spoonful into yoghurt, baby porridge, or warm water until thinned to a smooth paste
- Avoid crunchy peanut butter, dry peanut powder on the tongue (also choking risk)
- Aim for around 2 g of peanut protein per week (roughly 2 teaspoons of smooth peanut butter)
- Well-cooked egg first — hard-boiled, scrambled, in a baked good
- Cooked egg whites once well-tolerated
- Skip raw or undercooked egg in the first year (salmonella risk)
- Yoghurt, cheese, baked milk products from 6 months
- Cow's milk as a main drink not before 12 months
- Don't substitute "milk alternatives" (oat, almond, soy) as a main milk in this age — they don't replace cow's milk nutritionally
- Bread, pasta, baby porridge, breadsticks — usually one of the first foods introduced anyway
- Easy to incorporate
- Tahini paste smoothed thinly on a small piece of bread, or stirred into hummus
- Avoid whole sesame seeds (small choking risk)
- Smooth nut butter from one nut at a time (almond butter, cashew butter)
- Same principle as peanut — never whole nuts
- Cooked, deboned, finely flaked white or oily fish
- Limit oily fish (salmon, mackerel) to 4 portions per week max in girls and women, 2 portions in boys (mercury)
- Well-cooked, finely chopped, no shell pieces
- Often left until later in weaning — fine to introduce during the second 6 months
- Tofu, edamame (well-mashed), soy yoghurt
- Often introduced as part of family meals
What an Allergic Reaction Looks Like
The signs to watch for, in rough order from mild to severe:
Mild to moderate (urticaria-type reactions):- Hives — raised itchy red welts, often around the mouth or on the trunk
- Swelling of the lips, tongue, face, or eyes
- A few patches of red skin where food touched
- Vomiting
- Mild diarrhoea
- Difficulty breathing — wheeze, stridor, persistent cough, voice changes
- Swelling of the tongue or throat affecting breathing or speaking
- Pale, floppy, drowsy baby
- Significant drop in blood pressure (collapse)
Important note on milder reactions: redness and a few hives around the mouth from a food touching the skin (especially with high-acid foods like tomato, citrus, strawberry) are often contact reactions, not true allergy — they fade in 30 to 60 minutes and don't recur with the same food eaten properly. A genuine systemic reaction involves more than just the area where the food touched.
If a baby has hives or facial swelling but normal breathing, give the food and call the GP or 111 the same day. Don't give that food again until you've spoken to a clinician.
If breathing is affected, throat is swelling, or the baby is floppy/pale: 999, lay flat, do not stand up. If an EpiPen has been prescribed, use it (mid outer thigh, hold for 10 seconds).
Non-IgE Reactions Look Different
Not all food allergy presents as immediate hives. Some babies have delayed (non-IgE) reactions:
- Persistent eczema flares
- Persistent vomiting, reflux, or feed refusal
- Frequent loose, mucousy, or blood-streaked stools
- Failure to gain weight despite adequate feeding
- Excessive crying that pattern-matches with feeds
Cow's milk protein allergy (CMPA) commonly presents this way and is one of the more common allergies to recognise in the UK. If you suspect this, see your GP — assessment is clinical (no good blood test for non-IgE), and management is typically an elimination trial under guidance.
Eczema and Allergy
Babies with eczema have a higher rate of food allergy, and treating the eczema well — daily emollient, prompt steroid use during flares, NICE guidance for atopic eczema in children — is itself part of allergy prevention. Babies with severe eczema or existing egg allergy are the group where peanut introduction warrants a clinician's input first.
What Not to Do
- Don't delay introduction of allergens past 12 months unless specifically advised by an allergy clinician
- Don't introduce on holiday or far from medical help for the first time
- Don't introduce when the baby is unwell — fevers, vomiting, severe eczema flare — wait until things are settled
- Don't combine allergens at first introduction
- Don't rely on an antihistamine as a safety net during introduction — it can mask early signs
When to See an Allergy Clinician
Worth a referral via the GP if:
- Severe eczema in the under-6 months
- A clear allergic reaction to any food at any point
- A sibling with severe nut or other food allergy and you're worried about introducing
- Persistent feeding problems that haven't responded to GP-led measures (possible CMPA)
- Suspected oral allergy syndrome in older children (itching after fresh fruit; usually pollen-related)
NHS paediatric allergy services have variable waiting times. Private allergy testing exists; for IgE-mediated allergy, skin-prick testing and specific IgE blood tests are the main tools, but a positive test in a baby who has never eaten the food can mean sensitisation rather than allergy — interpretation needs a clinician.
Key Takeaways
The advice on allergen introduction reversed in the last decade. The 2015 LEAP trial showed that introducing peanut early to high-risk babies reduced peanut allergy by 81% compared to avoidance. Current NHS, BSACI, and NICE guidance: offer the major allergens — peanut, egg, cow's milk, wheat, sesame, fish, tree nuts, soy — from around 6 months alongside standard weaning, and keep offering them weekly to maintain tolerance. Babies with severe eczema or already-known egg allergy should have specialist allergy input before peanut introduction. Practical rule: one new allergen at a time, at home, during the day, watch for 2 hours.
