Introducing Allergens During Weaning
Although food allergy affects fairly low numbers of children in the UK, an estimated 5–8% of children, it is a common concern. IgE-mediated (immediate onset) food allergy, which can cause rapid onset reactions, is less common than non-IgE-(delayed onset) mediated allergy, but generates the greatest anxiety due to the potential for acute symptoms.
Although severe reactions are rare, uncertainty and fear of allergen introduction can lead to delayed or overly cautious feeding practices. It is not unusual to hear of parents taking their babies to hospital car parks to give them their first tastes of foods, usually nuts.
Current UK and Republic of Ireland guidance supports the introduction of the most common allergenic foods before the first birthday. Healthcare professionals play a key part in translating the guidance and relaying it as clear, consistent advice for families.
Providing structured, practical support can help reduce unnecessary avoidance, prevent over-medicalisation, and promote confident, varied feeding during weaning.
Current UK & RoI Guidance: What Healthcare Professionals Need to Know
The following recommendations are based on guidance from the Scientific Advisory Committee on Nutrition (SACN), the Committee on Toxicity (COT), the British Society for Allergy & Clinical Immunology (BSACI) and British Dietetic Association (BDA) Early Feeding Guidance, NICE clinical guidance, and the Health Service Executive (HSE) in Ireland.
Starting solids
Solids should be introduced when a baby is developmentally ready; able to sit upright in a highchair with good head control, able to coordinate food into the mouth with the hands and is able to swallow (has lost the tongue thrust reflex). For most babies this happens at around 6 months of age and should not be before 4 months (17 weeks).
Introduction of allergenic foods
Where possible, allergens should be introduced from the start of weaning; with all common allergenic foods being offered before the first birthday.
Common allergens to prioritise during weaning include:
- Cows’ milk (as an ingredient, not as a replacement for breastmilk or infant formula)
- Egg
- Peanut
- Tree nuts
- Wheat (gluten-containing cereals)
- Fish and shellfish
- Sesame
- Soya
Which infants are at higher risk of food allergy?
Most infants can introduce allergenic foods at home following standard weaning advice. However, a small proportion are at higher risk of developing food allergy and may require more individualised assessment.
Infants considered at higher risk include those:
- With moderate to severe eczema that started before 6 months
- Who already have a diagnosed food allergy
Why does eczema increase risk?
Babies with eczema are at higher risk of food allergy because the skin barrier is inflamed and broken, and tiny food particles from the environment can come into contact with the immune system through the skin. This can increase the risk of the body recognising that food as a threat rather than learning to tolerate it.
Early introduction can help to support the development of immune tolerance before sensitisation occurs. For this reason, timely introduction of allergenic foods is considered especially important in higher risk infants.
Defining moderate to severe eczema in practice
Eczema severity can be subjective, but features that may indicate higher risk include:
- Eczema present before 6 months of age
- Regular topical steroid treatment
- Poorly controlled eczema despite appropriate treatment
- Eczema affecting multiple body areas
Eczema should ideally be well controlled prior to allergen introduction, as active inflammation may make assessment of reactions more difficult.
Higher-risk infants: timing considerations
Infants at higher risk of food allergy, including those with moderate to severe eczema or an existing food allergy may benefit from the earlier introduction of cooked egg and peanut from 4 months of age.
Practical advice for higher-risk infants
For these infants:
- Population advice should still be followed, and solids should not be introduced before 4 months of age.
- Where possible, eczema should be optimally controlled prior to introduction.
- Routine screening prior to introduction is not recommended at a population level.
- Referral is indicated for infants with a history of immediate type reactions.
- Egg should be well cooked, with yolk and white mixed before offering.
- Peanut should be given ground or as smooth peanut butter, thinned with warm water if necessary to reduce choking risk.
- Parents can be advised to introduce the food earlier in the day when medical services are accessible.
- Parents should be given clear information about the signs of immediate allergic reactions and what action to take if they occur.
For many higher-risk infants, allergen introduction can still take place at home with appropriate assessment and safety-net advice.
What does not automatically increase risk?
- Presence of parental food allergy: food allergy presents as part of allergic atopy; an umbrella term for asthma, eczema, hay fever, food allergy and non-food allergy. Parental food allergy indicates an increased risk of one of these conditions.
- Having a sibling with food allergy: Parents of infants with a food-allergic sibling often delay allergen introduction due to understandable anxiety. However, current evidence suggests that this delay may increase the likelihood of developing food allergy rather than prevent it.
- Mild, well-controlled eczema: is less likely to have led to sensitisation through the skin.
How to introduce allergens safely
For most babies, home introduction of allergenic foods as part of normal weaning is recommended.
Step 1: Ensure developmental readiness
Allergen introduction should take place once the infant is developmentally ready for solids, around 6 months and not before 4 months. Signs of readiness include:
- Sitting with support and holding the head steady
- Coordinating items into the mouth with the hands
- Swallowing food rather than pushing it out with the tongue (tongue thrust reflex)
Step 2: Introduce one allergen at a time
Allergens should be introduced one at a time; so if a reaction occurs it is easy to identify the cause.
A practical approach is to:
- Start with a small amount (e.g. a small spoonful mixed into a tolerated food).
- Increase gradually over 2–3 days while monitoring for symptoms.
- Avoid introducing other new allergens during this period.
Step 3: Maintain regular exposure
Introducing a food once and then not offering it again is unlikely to support ongoing tolerance. This may be particularly important for families whose diet does not regularly include some allergens (for example, plant-based families), where intentional inclusion may need to be planned.
Step 4: Offer allergens in safe, age-appropriate forms
Whilst discussing allergy safety, it is important to also consider other potential risks such as choking.
Examples include:
- Egg: Well-cooked (e.g. hard-boiled or well-cooked omelette), ensuring both yolk and white are combined and fully cooked. Offer pureed, mashed or as finger food.
- Peanut: Smooth peanut butter thinned with warm water, breastmilk or formula; or peanut powder/ground peanut mixed into purée.
- Tree nuts: Ground nuts or smooth nut butters. Never whole or coarsely chopped nuts due to choking risk. Tree nuts contain different proteins. Where possible, introduce different nuts individually in ground or smooth forms as part of normal weaning.
- Milk: As an ingredient (e.g. yoghurt, cheese, milk in cooking). Whole cows’ milk should not be given as a main drink before 12 months as it may displace a breast or formula feed.
- Wheat: Cereal, bread or pasta in age-appropriate textures.
- Sesame: Tahini, sesame oil or hummus (ensuring smooth consistency).
- Fish: Well-cooked and flaked carefully to remove bones. Different types of fish contain different proteins, so new varieties should be introduced individually in the same way as other new foods.
Practical points:
- Introduce new allergens earlier in the day rather than before bedtime.
- Ensure baby is well at the time of introduction.
- Reassure that most infants tolerate allergens without difficulty and that even if a reaction occurs it is less likely to be an immediate onset, severe reaction.
- After peanuts and tree nuts have been introduced and tolerated, an easy way to maintain regular tolerance is to finely grind mixed nuts and add to foods. These should be prepared in small batches, as ground nuts can become rancid quickly. Whole or chopped nuts should be avoided to choking risk.
Recognising Allergic Reactions
When supporting families with the introduction of solids, it can be helpful to explain the difference between immediate (IgE-mediated) and delayed (non-IgE-mediated) food allergy. This helps parents understand what to monitor for and reduces unnecessary anxiety about normal feeding behaviours.
Immediate (IgE-mediated) food allergy
IgE-mediated reactions usually occur within minutes, and typically within around 2 hours of eating.
Mild to moderate symptoms may include:
- Urticaria (hives)
- Swelling of the lips, face or eyes (angioedema)
- Vomiting
- Sudden onset of redness or itching
Anaphylaxis
Anaphylaxis is much less usual but requires urgent action. These can be remembered using the ABC approach:
- Airway: Persistent cough, hoarse cry, swollen tongue
- Breathing: Difficult or noisy breathing, wheeze
- Circulation/Consciousness: Pale, floppy, drowsy, unresponsive or unconscious
Parents should call an ambulance if ABC symptoms occur so that adrenaline can be given.
Delayed (non-IgE-mediated) food allergy
Delayed-type reactions typically occur within an hour or two up to several days after ingestion.
Symptoms may include:
- Recurrent vomiting or reflux
- Abdominal pain
- Blood in stools
- Mucus in stools
- Persistent diarrhoea or constipation
- Worsening eczema
- Feeding aversion
Delayed-type allergy does not cause anaphylaxis.
Reassurance and differentiation
It is also important to reassure parents that not all skin changes after eating are allergic reactions. Redness or mild skin irritation localised to the face is common and does not indicate food allergy.
Providing clear, structured information about what constitutes a true allergic reaction can reduce unnecessary anxieties and food restriction.
What To Do If a Reaction Occurs
If symptoms are suggestive of an allergic reaction when a new food is given, the suspected trigger food should be avoided until further assessment has taken place.
Immediate (IgE-mediated) reactions
Immediate reactions typically occur within minutes, and usually within 2 hours, of eating the food.
If symptoms suggest an immediate allergic reaction:
- Avoid giving the suspected trigger food.
- Advise seeing GP for further assessment.
- An allergy-focused history should be taken and referral to specialist services considered where appropriate.
If severe symptoms develop — particularly airway, breathing or circulation symptoms (ABC) parents should be advised to seek urgent medical assistance by calling emergency services.
Delayed (non-IgE-mediated) reactions
Delayed reactions usually develop several hours up to days after eating the food.
If delayed symptoms are suspected:
- Stop the suspected trigger food.
- If symptoms were mild and settle quickly, cautious reintroduction of the food may be considered after 1–2 weeks, as recurring symptoms can assist with effective diagnosis.
- If symptoms recur, persist, or are more severe, GP review is recommended.
Referral for specialist assessment may be appropriate where symptoms are persistent, severe, or associated with faltering growth.
Delayed-type food allergy does not cause anaphylaxis.
Supporting families and reducing anxiety
Experiencing an allergic reaction can be extremely worrying for parents. Clear guidance from healthcare professionals can help families respond appropriately while avoiding unnecessary long-term food exclusion. Thinking about the following areas can also go a long way to helping families to work through their worries:
- Normalise concern: Acknowledge that worry about allergy is common and understandable. Validating these feelings will help families to feel supported.
- Ensure parents feel heard: Many parents dealing with food allergy report that their worries are minimised or misunderstood. Creating space, where appropriate, for parents to discuss their child’s symptoms and fears is a valuable part of the care provided.
- Provide clear, consistent messages: Emphasise that unless advised otherwise, early, introduction is recommended and that most infants tolerate allergens.
- Avoid over‑medicalisation: Reassure that hospital‑based first exposures are rarely necessary in the absence of clear high‑risk features.
Encourage positive feeding experiences: Support families to focus on variety, enjoyment and family mealtimes. Feeding can still be a positive experience even when food allergies are present.
Addressing Common Myths in Practice
The introduction of allergens is an area often affected by misinformation and common myths. Some of the misconceptions that might come up in clinical practice are set out below.
Myth 1: It is safest to screen before allergen introduction, just to be sure
Routine screening before introducing allergens is not recommended; it does not show up delayed reactions. Inappropriate testing can lead to increased anxiety, delay introduction of foods and may lead to unnecessary dietary restriction.
Testing may identify sensitisation without confirming clinical allergy, which means some babies may end up avoiding foods they tolerate. Testing is most helpful when guided by a relevant clinical history and when results can be interpreted by a clinician with appropriate expertise.
Myth 2: A food only needs to be offered once
Introducing a food once is not enough, it should be given for several days. Once tolerated, allergenic foods should be given every week as part of a baby’s normal diet to help with ongoing tolerance.
Myth 3: A negative allergy test rules out food allergy
A negative skin prick test or specific IgE test makes IgE-mediated food allergy less likely, but it does not exclude delayed (non-IgE-mediated) food allergy. Gold standard for assessing allergies is removal of a food following symptoms, and if symptoms are recurring with reintroduction of that food an allergy is confirmed. Any test results should be interpreted alongside an allergy focussed history.
Myth 4: Home allergy or intolerance tests are a reliable way to diagnose food allergy
Commercial home tests are not recommended for diagnosing food allergy as they are often not evidence based or accurate. Diagnosis should be based on an allergy-focused clinical history and, where appropriate, validated testing interpreted by an appropriately trained clinician.
Key takeaways:
Most infants can begin solids at around 6 months and not before 4 months. All common allergenic foods should be introduced before 12 months as part of normal weaning.
Early‑onset moderate–severe eczema and existing food allergy are the strongest predictors of allergy. These babies would benefit from early introduction from 4 months.
Introduce one allergen at a time, in small amounts, and increase gradually over 2–3 days. Use safe textures (e.g., smooth nut butters, well‑cooked egg) and have ongoing regular exposures.
Although it can feel scary introducing foods for the first time, reassure parents that a small number of babies have allergic reactions; and of that number most are delayed onset reactions.
Routine screening before allergen introduction is not recommended. Test results must always be interpreted alongside an allergy focused clinical history.
Normalise concerns and offer practical advice. Emphasise that early, varied feeding supports long term tolerance.
Where possible, aim to refer infants with suspected IgE‑mediated reactions, persistent or severe delayed symptoms, faltering growth, or complex feeding concerns to specialist allergy services.
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Written by Lucy Wood
Lucy has a BSc honours degree from King’s College London with additional postgraduate learning through the British Dietetic Association and has been working as a registered dietitian for 12 years both within the NHS and the private sector.
