Allergies in babies look different from allergies in adults, and they often look different from what parents expect. Recognising the signs — and knowing what does and doesn't point to allergy — helps avoid both missing a real problem and over-medicalising normal variation.
For a comprehensive overview, see our complete guide to child health.
What Baby Allergies Look Like
Allergies in infants typically fall into two categories based on how quickly symptoms appear:
IgE-mediated (immediate) reactions: These occur within minutes to 2 hours of exposure. Symptoms include urticaria (hives — raised, itchy red welts), swelling (particularly of the face, lips, or tongue), vomiting, and in severe cases, difficulty breathing or circulatory collapse (anaphylaxis). These are the "classic" allergy reactions and are usually obvious in their timing and nature.
Non-IgE-mediated (delayed) reactions: These occur hours to days after exposure, making the link to a trigger harder to spot. They present as: eczema flares, persistent vomiting, diarrhoea or blood in stools (in infants), colicky abdominal pain, and faltering growth. These are more common in infants than immediate reactions.
Cow's Milk Protein Allergy (CMPA)
The most common food allergy in infants, affecting around 2–3% of babies. It can be IgE-mediated (immediate) or non-IgE-mediated (delayed). Key features:
In formula-fed babies: Symptoms begin when formula is introduced. Persistent vomiting, reflux that doesn't respond to usual measures, blood-streaked stools, eczema, and significant distress after feeds may all indicate CMPA.
In breastfed babies: Cow's milk proteins from the mother's diet pass into breast milk in small amounts. A small proportion of breastfed babies react to this. The symptoms are similar — significant eczema, colicky distress, mucousy or bloody stools — but the diagnosis requires eliminating dairy from the mother's diet for 2–4 weeks as a diagnostic trial.
Management: Cow's milk must be removed from the baby's diet (or the breastfeeding mother's diet). For formula-fed babies, an extensively hydrolysed formula (eHF) — where the milk proteins are broken into small pieces — is usually tolerated. Amino acid-based formula is used in more severe cases.
Most children outgrow CMPA by 3–5 years of age.
Eczema and Allergy
Atopic eczema is the most common allergic condition in infants. It presents as dry, itchy, inflamed skin — typically on the cheeks, scalp, and arm creases in young babies. It is associated with a general tendency toward allergic conditions (atopic march), but most eczema in babies is not driven by a specific food allergy.
However, severe eczema that doesn't respond to standard topical treatment, or eczema that flares consistently after feeding, may have a dietary trigger worth investigating.
Allergy testing (skin prick testing or specific IgE blood tests) is not routinely indicated for all babies with eczema, but is appropriate when there is a pattern suggesting a food trigger, or in severe eczema.
Egg Allergy
Egg allergy is the second most common food allergy in infants. It typically presents as a skin reaction (hives, eczema flare) or vomiting shortly after the first exposure to egg. Most children outgrow egg allergy by 5 years, though egg allergy in children with significant eczema is more persistent.
Babies with egg allergy can usually receive all routine vaccinations (including MMR, which contains trace egg proteins) safely. Advice varies for yellow fever and influenza vaccines; discuss with the vaccinating clinician if relevant.
When to Seek Medical Help
Seek urgent help (999 or A&E) for: difficulty breathing, audible wheeze or stridor, severe swelling of the face or mouth, collapse or sudden pallor, following any food exposure.
Seek a GP appointment for: persistent eczema not responding to emollients and mild topical steroids, recurring vomiting or diarrhoea after feeds, blood in stools without an obvious cause, or failure to thrive with concerns about diet.
Referral to a paediatric allergist is indicated for confirmed or suspected food allergy requiring ongoing management, children who have had anaphylaxis, and multiple food allergies.
Avoiding the Over-Diagnosis Trap
Not every skin reaction is an allergy. Not every bout of vomiting points to food. The most common responses — giving every baby a dairy-free diet "just in case" or eliminating multiple foods from a breastfeeding mother's diet without clear evidence — can create nutritional deficiencies without benefit. A structured approach, with GP input where needed, gives a more accurate picture.
Key Takeaways
Allergies in babies present as either IgE-mediated (immediate) reactions with hives and swelling, or non-IgE-mediated (delayed) reactions with eczema, vomiting, or diarrhoea over days. Cow's milk protein allergy is the most common food allergy in infants, affecting 2-3% of babies. Severe eczema not responding to standard topical treatment may indicate a dietary trigger worth investigating. Seek urgent help for difficulty breathing, severe swelling, or collapse; seek GP care for persistent eczema, recurring vomiting after feeds, or failure to thrive.
