Weaning Your Baby: Why Early Allergy Screening is the New Standard
⚡ Quick Answer
If your baby has eczema, a family history of allergies, or you're planning early weaning, proactive allergy screening can help identify sensitisation to common triggers like nut allergy and egg before you introduce them. A specific IgE blood test measures your baby's immune response without exposing them to allergens — but results must be interpreted alongside clinical history. Testing supports a clinician's assessment; it doesn't replace it.
🚨 When to Seek Urgent Help
Call 999 or go to A&E immediately if your baby or child develops any of the following after eating a new food:
- Difficulty breathing, wheezing, or noisy breathing
- Swelling of the tongue, lips, or throat
- Becoming floppy, pale, or unresponsive
- Widespread hives or flushing spreading rapidly across the body
- Persistent vomiting shortly after eating
- Sudden drowsiness or limpness in an infant
These can be signs of anaphylaxis — a life-threatening allergic reaction that can occur even on first known exposure. If your child has been prescribed an adrenaline auto-injector, use it immediately and still call 999. Do not wait to see if symptoms improve on their own.
The Science Behind Baby Food Allergies — in Plain English
What is an IgE-mediated food allergy?
When your baby eats a food like peanut or egg for the first time, their immune system assesses the proteins in that food. In most babies, the immune system recognises them as harmless and moves on. But in some, it produces a specific antibody called Immunoglobulin E (IgE) against those proteins.
On subsequent exposure, these IgE antibodies trigger mast cells to release histamine and other chemicals — potentially causing reactions ranging from hives and egg allergy symptoms like facial swelling, to more serious responses including breathing difficulty and anaphylaxis. This is an IgE-mediated food allergy: rapid in onset (usually within minutes to two hours), immune-driven, and potentially serious.
It's quite different from a food intolerance or non-IgE-mediated allergy (which tends to cause delayed gut symptoms). When we talk about nut allergy in infants, we're almost always referring to this IgE-mediated pathway — and it's exactly what specific IgE blood tests are designed to detect.
Sensitisation vs clinical allergy — the crucial distinction
This is where many parents understandably get confused. Your baby can have detectable IgE to a food — say peanut or egg — without ever having had a reaction. This is called sensitisation. It means the immune system has noticed the protein, but it doesn't guarantee a clinical reaction will occur.
Equally, a negative IgE result is reassuring but doesn't absolutely rule out allergy — particularly in very young infants whose immune systems are still maturing.
This is precisely why test results must be interpreted alongside clinical history — what symptoms appeared, how quickly, and what the baby had eaten. A baby allergy test provides objective data that supports a clinician's assessment. It doesn't diagnose on its own. No single blood value can confirm or exclude a food allergy without context.
Why eczema in babies raises the allergy conversation
There's a well-established link between eczema in babies and food allergy. Research shows that infants with moderate-to-severe eczema — particularly when it appears in the first few months of life — have a significantly higher risk of developing IgE-mediated food allergies, especially to egg and peanut.
The current thinking is that a disrupted skin barrier (as seen in eczema) may allow food proteins to enter through the skin, priming the immune system to react against them. This is why clinical guidelines now specifically highlight babies with eczema as a group that may benefit from proactive allergy screening before introducing common allergens during weaning.
Why Proactive Screening During the Weaning Window Matters
For years, the standard advice was to delay introducing allergenic foods — avoid peanut until age three, hold off on egg until twelve months. That guidance has been completely overturned by landmark research.
The LEAP trial (Learning Early About Peanut Allergy) demonstrated that early introduction of peanut — from around 4–6 months — actually reduced the risk of developing peanut allergy by up to 81% in high-risk infants. The EAT study showed similar benefits for early egg introduction. Current UK guidance from BSACI and the NHS now recommends introducing allergenic foods from around six months (or after four months if early weaning is advised by a healthcare professional), one at a time.
But here's the challenge: how do you confidently introduce peanut or egg if your baby already has significant eczema or a family history of nut allergy? This is where a proactive baby allergy test fits in.
A specific IgE blood test taken before you start weaning with high-risk allergens gives you and your clinician baseline data. If the results show no sensitisation, you can introduce those foods with greater confidence. If sensitisation is detected, your clinician can plan a supervised introduction — typically in a clinical setting — rather than you discovering an allergy at home during a first taste.
This is the content gap that most competitor advice misses. They focus on reactive treatment — what to do after a reaction has happened. Proactive screening during the critical weaning window helps you and your clinician plan ahead rather than respond to a crisis.
Your Options Compared: Blood Test vs Skin Prick for Babies
Both testing methods can play a role in assessing food allergies in infants. However, for young babies — particularly those with eczema — a blood test offers clear practical advantages as a first-line assessment:
| Factor | Specific IgE Blood Test | Skin Prick Test (SPT) |
|---|---|---|
| What it measures | IgE antibodies to specific food proteins in blood | Skin wheal response to applied food extract |
| Allergen exposure during test | None — blood sample only | Yes — small amount of allergen applied to skin |
| Risk of reaction during test | No risk of allergic reaction | Very small risk — must be done near resuscitation facilities |
| Antihistamine use | No need to stop — does not affect results | Must stop antihistamines days beforehand |
| Where it's done | Any clinical setting with phlebotomy (nurse-led blood draw) | Specialist allergy clinic only |
| Turnaround time | Typically 5–7 working days | Results within 15–20 minutes |
| Skin condition impact | Unaffected by eczema or skin inflammation | Often unreliable in babies with eczema — inflamed skin can cause false positives |
| Suitability for infants | Suitable from a few months of age — single blood draw | Can be distressing; requires the infant to stay still; limited skin surface area |
| Multiple allergens | Can test many allergens from one blood sample | Each allergen requires a separate skin prick |
| Best suited for | Pre-weaning screening, babies with eczema, proactive assessment before food introduction | Specialist-led diagnostic workup, usually after blood testing |
For babies with eczema — the very group most likely to need allergy testing — skin prick testing is often less reliable because inflamed or broken skin can produce misleading results. A specific IgE blood test is typically the most practical and reliable first step in infants: one blood draw can screen for multiple allergens, it's unaffected by skin condition or antihistamine use, and there's zero risk of triggering an allergic reaction during the test itself.
What Baby Allergy Test Results Can (and Can't) Tell You
Interpreting positive results in infants
A positive specific IgE result (typically >0.35 kU/L) indicates sensitisation to the tested food. In an infant who has already reacted to that food, this strongly supports a diagnosis of IgE-mediated allergy.
In a baby who has never been exposed to the food, a positive result tells you sensitisation has occurred — likely through skin exposure (particularly common in babies with eczema) — and that introduction of that food should be discussed with a clinician rather than attempted at home without guidance. This is proactive screening at its most useful.
Higher IgE levels are associated with a greater probability of clinical reactivity, but they do not reliably predict how severe a reaction might be. A baby with a very high peanut IgE might have mild hives, while one with a lower level could potentially have a more significant reaction. Context matters more than numbers.
Understanding negative results
A negative result is reassuring and suggests the baby is unlikely to have an IgE-mediated allergy to that food at the time of testing. However, it's not an absolute guarantee — particularly in very young infants whose immune systems are still developing. IgE levels can change over time.
If a baby has a convincing history of reacting to a food but tests negative, further evaluation (possibly including supervised oral food challenge) may be recommended by a specialist.
Cross-reactivity in common weaning foods
Cross-reactivity is relevant during weaning. For example, a baby sensitised to peanut (a legume) may also show positive IgE to other legumes like soya or lentils — but this doesn't necessarily mean they'll react clinically to those foods. Similarly, egg white and egg yolk contain different proteins; a baby may be allergic to one component but tolerate the other, particularly when well-cooked (heat denatures some egg proteins).
Nut allergy cross-reactivity is particularly important. Peanut is a legume, not a tree nut, so peanut allergy doesn't automatically mean your baby needs to avoid all tree nuts. Component-resolved blood testing can help distinguish genuine multi-food sensitisation from cross-reactivity — information that directly prevents unnecessary dietary restriction in growing infants.
Can a test number predict anaphylaxis risk?
In short — no. A higher IgE level does not reliably predict a more severe reaction in your baby. The anaphylaxis risk from a given food depends on many factors: the amount eaten, how it was prepared, whether the baby was unwell at the time, and individual immune factors that blood tests cannot fully capture.
This is why decisions about food introduction, adrenaline auto-injector prescriptions, and specialist referrals are always based on clinical history combined with test results — never test numbers alone.
Practical Next Steps: Your UK Pathway
If you're approaching the weaning stage and concerned about food allergies — or your baby already has eczema and you want to introduce allergens safely — here's a sensible approach:
Keep a symptom and food diary
Note any skin flare-ups, digestive symptoms, or reactions — what your baby ate, when symptoms appeared, and how long they lasted. Photos of rashes or swelling are genuinely helpful for clinicians. If your baby has eczema, record its severity and any patterns you notice around feeding.
Consider a specific IgE blood test before introducing high-risk foods
A specific IgE blood test can screen for sensitisation to common weaning allergens — peanut, tree nuts, egg, milk, wheat, soya, fish, and sesame — from a single blood sample. It's a nurse-led blood draw: no allergen exposure, no need to stop any medication, and suitable for infants. Results give you and your GP objective data to plan introductions safely.
Avoid unnecessary elimination diets
Removing foods from a baby's diet without clinical guidance can do more harm than good. Unnecessary restriction during weaning can affect nutrition, growth, and even increase the risk of developing allergies (by removing the tolerance-building exposure). Always discuss any dietary exclusions with your GP, health visitor, or dietitian — ideally with test data to support the conversation.
Discuss results with a clinician and plan introductions
Take your test results and food diary to your GP or health visitor. If sensitisation is found, they can arrange a specialist referral for supervised food challenges if appropriate. If results are negative, you can introduce those foods at home with confidence — starting with small amounts, one new food at a time, and watching for any reaction over the following hours.
Frequently Asked Questions
At what age can a baby have an allergy blood test?
A baby allergy test using specific IgE blood testing can be performed from a few months of age. There's no minimum age restriction for the blood test itself. In practice, testing is most commonly considered from around 3–4 months onwards, particularly in infants with moderate-to-severe eczema or a strong family history of allergies, as this aligns with the period just before early weaning typically begins.
What are the most common egg allergy symptoms in babies?
Egg allergy symptoms in babies typically appear within minutes to two hours of eating egg and may include: hives or red welts around the mouth or body, facial swelling (particularly lips and eyes), vomiting, eczema flare-up, or in more severe cases breathing difficulty. Some babies tolerate well-cooked egg (in cakes or biscuits) but react to lightly cooked or raw egg, because cooking denatures some of the allergenic proteins.
Does eczema in babies mean they'll have a nut allergy?
Not necessarily, but there is a significant link. Babies with moderate-to-severe eczema — particularly when it appears before six months — have a higher risk of developing food allergies including nut allergy. Research suggests the disrupted skin barrier allows food proteins to sensitise the immune system through the skin. This is precisely why proactive screening before weaning is now recommended for this group, so introductions can be planned with data rather than guesswork.
Should I delay introducing peanut and other nuts to my baby?
Current UK guidance says no. Delaying allergen introduction beyond 6–12 months may actually increase the risk of developing allergies. The LEAP trial showed that early peanut introduction (from around 4–6 months in high-risk babies) reduced peanut allergy by up to 81%. Current advice is to introduce allergenic foods from around six months, one at a time. If your baby has significant eczema or a family history of allergies, discuss with your GP whether a blood test beforehand would be helpful.
What's the difference between a food allergy and a food intolerance in babies?
A food allergy involves the immune system (IgE-mediated) and can cause rapid, potentially serious reactions — hives, swelling, breathing problems, anaphylaxis. A food intolerance (like lactose intolerance) doesn't involve IgE and typically causes delayed digestive symptoms — bloating, wind, loose stools. IgE blood tests detect immune-mediated allergies, not intolerances. If you're unsure which your baby might have, discussing symptoms with your GP is the best first step.
Can my baby outgrow a nut allergy?
It depends on the specific allergy. Around 20% of children with peanut allergy outgrow it by school age, and the majority of children with egg and milk allergy do outgrow them. Tree nut allergies tend to be more persistent. Periodic re-testing (usually annually or as recommended by a specialist) can track whether IgE levels are declining — a sign that tolerance may be developing. Any re-introduction should be supervised by a clinician, never attempted at home without guidance.
Is a blood test or skin prick test better for babies?
For most infants — especially those with eczema in babies — a specific IgE blood test is generally the more practical first-line option. It requires only one blood draw (testing multiple allergens from a single sample), isn't affected by skin condition or antihistamines, and carries no risk of triggering an allergic reaction. Skin prick testing can be useful as a follow-up in specialist settings but is often less reliable in babies with inflamed skin and can be more distressing for very young infants.
How do I safely introduce peanut to my baby during weaning?
Never give whole or chopped nuts to babies or young children (choking risk). Instead, use smooth peanut butter thinned with breast milk, formula, or water, or peanut puffs designed for infants. Start with a tiny amount (e.g., the tip of a teaspoon), offer it early in the day when you can observe for reactions, and wait a few hours before introducing anything else new. If your baby has eczema or a family history of allergies, consider a baby allergy test beforehand and discuss the plan with your GP.
What is the anaphylaxis risk when introducing allergens during early weaning?
Severe anaphylaxis during first food introduction is uncommon but not impossible. The anaphylaxis risk is higher in babies who are already sensitised (detectable IgE) — which is one reason proactive screening can be valuable. If a blood test shows significant sensitisation, first introduction can be planned in a clinical setting with medical supervision. For babies with no sensitisation and no prior reactions, home introduction following standard guidance carries a very low risk.
Do I need to stop my baby's antihistamines before a blood test?
No. Unlike skin prick testing, specific IgE blood tests are not affected by antihistamines or any other medication. If your baby is taking antihistamines for eczema or another condition, you can continue them as normal. This is one of the key practical advantages of blood testing in infants who are often on regular medication for their skin.
Summary
The science is clear: early introduction of allergenic foods during weaning reduces allergy risk. But for babies with eczema, a family history of allergies, or other risk factors, knowing before you introduce those foods whether sensitisation exists can make all the difference between a calm, planned introduction and a frightening first reaction.
A specific IgE blood test is the most practical first step for infant allergy screening. It's safe (no allergen exposure), unaffected by eczema or antihistamines, and can test for multiple common allergens from a single blood sample. It gives you and your clinician objective data to guide weaning decisions — not replace clinical judgement, but meaningfully support it.
Proactive screening during the weaning window is not about creating anxiety. It's about replacing uncertainty with information, so you can introduce foods confidently and seek specialist support early if needed — rather than discovering an allergy during an unplanned reaction at home.
Thinking About Screening Before You Start Weaning?
Our nurse-led service makes infant allergy blood testing straightforward. A single venous blood draw — no allergen exposure, no need to stop any medication — with results typically within 5–7 working days. Browse our panel options to see what's available, and discuss with your GP or health visitor which allergens to test for.
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References
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- Du Toit G et al. Randomized trial of peanut consumption in infants at risk for peanut allergy (LEAP study). New England Journal of Medicine, 2015;372(9):803–813.
- Perkin MR et al. Randomized trial of introduction of allergenic foods in breast-fed infants (EAT study). New England Journal of Medicine, 2016;374(18):1733–1743.
- BSACI — Guidelines for the diagnosis and management of food allergy. bsaci.org
- NICE — Food allergy in under 19s: assessment and diagnosis (CG116). nice.org.uk
- Lack G. Epidemiologic risks for food allergy. Journal of Allergy and Clinical Immunology, 2008;121(6):1331–1336.
- Allergy UK — Weaning and food allergy. allergyuk.org
- Anaphylaxis UK — Food allergy in children. anaphylaxis.org.uk
- Boyce JA et al. Guidelines for the diagnosis and management of food allergy in the United States. Journal of Allergy and Clinical Immunology, 2010;126(6):S1–S58.
- Turner PJ et al. Can we identify patients at risk of life-threatening allergic reactions to food? Allergy, 2016;71(9):1241–1255.