How to Introduce the Top Allergens When Weaning Your Baby

The question of when and how to introduce allergenic foods to a baby is one that causes considerable anxiety for many parents. Reassuringly, the evidence over the past decade has shifted significantly: we now know that early, regular introduction of allergenic foods is associated with a lower risk of allergy developing, not a higher one. Delaying introduction does not protect against allergy — in many cases, it increases the risk.

The Evidence Base for Early Introduction

The landmark LEAP (Learning Early About Peanut Allergy) trial, published in 2015, showed that introducing peanuts to high-risk infants early and regularly reduced the risk of peanut allergy by around 80% compared to avoidance. Subsequent research, including the EAT (Enquiring About Tolerance) trial in the UK, reinforced the principle that early introduction of allergenic foods during the weaning window confers protection.

Current NHS guidance, in line with the Scientific Advisory Committee on Nutrition, recommends introducing allergenic foods from around 6 months of age (and not before 4 completed months). Once a food has been introduced without a reaction, it should be continued regularly to maintain tolerance.

A Note on High-Risk Babies

Babies with a personal history of eczema or a first-degree relative (parent or sibling) with a diagnosed food allergy are at higher risk of developing food allergies themselves. If your baby has severe or persistent eczema, or has already reacted to a food, speak to your GP or health visitor before introducing peanuts or other high-risk allergens. You may be referred to an allergy clinic for supervised introduction.

For most babies with no significant risk factors, introducing allergens at home is appropriate and recommended.

The 14 Major Allergens

EU and UK food labelling law requires the 14 major allergens to be highlighted on pre-packaged food. These are:

1. Peanuts
2. Tree nuts (almonds, hazelnuts, walnuts, cashews, pecans, pistachios, Brazil nuts, macadamias)
3. Milk (cow's milk protein)
4. Eggs
5. Wheat (gluten)
6. Fish (various species)
7. Crustaceans (prawns, crabs, lobster)
8. Molluscs (squid, mussels, oysters, scallops)
9. Sesame
10. Soya
11. Celery
12. Mustard
13. Lupin
14. Sulphur dioxide and sulphites

In practice, the allergens of greatest clinical significance in babies are peanuts, tree nuts, milk, eggs, wheat, sesame, and soya. Fish and shellfish are also significant but tend to be introduced slightly later in the weaning journey as they are less common first foods.

How to Introduce Each Allergen Safely

Introducing one at a time: When introducing a new allergenic food, it is advisable to give it on its own (or mixed into a plain food your baby already tolerates) so that if a reaction occurs, you know which food caused it. Wait 2–3 days before introducing the next new allergen.

Start with a small amount: Offer a small taste — perhaps a quarter of a teaspoon — on the first introduction. If there is no reaction, you can offer more at the next sitting.

Introduce at home, during the day: Introduce new allergens in the morning or early afternoon, at home, so you can observe your baby for a couple of hours and can access medical care easily if needed. Do not introduce a new allergen before bed or just before leaving the house.

Continue regularly once introduced: Once tolerated, continue to include the food in your baby's diet at least 3 times per week. Regular exposure is what builds and maintains tolerance.

Peanuts

Whole peanuts and large pieces are a choking hazard for children under five. Instead, offer smooth peanut butter (no added salt or sugar) thinned with a little milk or pureed fruit, or peanut butter dissolved in a sauce. Puffed peanut snacks designed for babies are also available.

Tree Nuts

As with peanuts, whole or roughly chopped nuts are not appropriate. Finely ground almonds can be mixed into porridge or yoghurt. Individual nut butters (almond, cashew) can be introduced in the same way as peanut butter.

Cow's Milk

While cow's milk should not be given as a main drink until 12 months, it can and should be included in cooking and in dairy foods from 6 months. Yoghurt, soft cheese, and cow's milk used in sauces are appropriate ways to introduce this allergen during weaning.

Eggs

Eggs must be cooked until both the white and yolk are solid for babies. Scrambled eggs, hard-boiled eggs, or egg cooked into pancakes or frittata are all suitable. Once well-cooked egg is tolerated, lightly cooked egg can be introduced.

Wheat

Bread, pasta, and porridge made with wheat are the simplest ways to introduce gluten. Offer a small amount of toast, soft pasta, or wheat-based baby porridge as early foods.

Sesame

Tahini (sesame paste) mixed into a vegetable puree or yoghurt is an easy way to introduce sesame. Hummus, which contains tahini, is another option once your baby is having a more varied diet.

Soya

Tofu, edamame beans, and foods cooked with soya are appropriate ways to introduce this allergen. Note: babies with cow's milk protein allergy have an elevated risk of soya allergy too, so speak to your GP before introducing soya if CMPA is confirmed.

Fish

White fish such as cod, haddock, or salmon — well-cooked and carefully checked for bones — can be introduced from around 6 months. Aim to offer fish at least twice a week (including oily fish once a week) for the broader nutritional benefits as well as allergen introduction.

Crustaceans and Molluscs

These tend to be introduced later in the first year, once your baby is eating a wider range of foods. Ensure shellfish is very fresh, thoroughly cooked, and served in a form without shell fragments.

What to Watch For: Signs of an Allergic Reaction

Most allergic reactions in babies are mild. Symptoms typically appear within a few minutes to two hours of eating the food:

Mild to moderate symptoms:

• Skin: redness, hives (raised, itchy welts), mild facial swelling
• Gut: vomiting, diarrhoea, abdominal discomfort
• Eyes or nose: itching, runny nose, watering eyes

Severe symptoms (anaphylaxis — call 999 immediately):

• Swelling of the tongue or throat
• Hoarse voice or unusual cry
• Difficulty breathing, wheeze, or persistent cough
• Pale, floppy, or unresponsive
• Sudden deterioration

If your baby shows any signs of a mild reaction, stop the food, give it no more on that occasion, and contact your GP for advice before trying again. If you observe any signs of a severe reaction, call 999 immediately.

Keeping a Record

Many parents find it helpful to keep a simple food diary during the allergen introduction phase. Note the date, the food offered, the amount, and any symptoms observed. This record is invaluable if you need to discuss a potential reaction with your GP or allergy clinic.