Signs of Food Allergy in Babies: What Parents Need to Know

Why food allergy is common in babies

Food allergy affects around 5–8% of children in the UK, with the highest rates in infancy. Babies are particularly vulnerable because their immune systems are still developing and their gut barrier is immature. The most common food allergens in babies are cow's milk, egg, peanut, wheat, and soy. Most food allergies in infancy present within the first year of life — often when a new food is introduced for the first time.

Immediate (IgE-mediated) reactions — what to look for

Immediate allergic reactions typically occur within minutes to 2 hours of eating the trigger food. Signs in babies include:

• Hives (urticaria) — raised, red, itchy welts on the skin
• Redness or flushing of the skin, particularly around the mouth
• Swelling of the lips, tongue, or face
• Vomiting shortly after feeding
• Runny nose or sneezing
• Watery or red eyes
• Coughing, wheezing, or noisy breathing
• Becoming pale, floppy, or unusually drowsy — signs of anaphylaxis requiring immediate 999 call

Delayed (non-IgE-mediated) reactions — harder to spot

Non-IgE-mediated food allergy causes delayed reactions, typically 2–72 hours after eating. These are more common in infants and are often missed because the link between the food and the symptom is not obvious. Signs include:

• Persistent reflux or vomiting that does not respond to standard treatment
• Loose, frequent, or mucousy stools
• Blood or mucus in the nappy
• Excessive crying, colic, or irritability — particularly after feeds
• Faltering growth or poor weight gain
• Eczema that is difficult to control with standard treatment
• Constipation (less common but recognised)

Eczema as a sign of food allergy

Eczema is one of the most important early signs of food allergy in babies. Around 30–40% of infants with moderate-to-severe eczema have an underlying food allergy — most commonly cow's milk or egg — that is driving or worsening their skin condition. If your baby's eczema is not responding well to standard treatment, allergy testing is recommended.

Cow's milk allergy — the most common food allergy in infants

Cow's milk protein allergy (CMPA) is the most common food allergy in babies, affecting 2–3% of infants. It can cause both immediate and delayed reactions. In formula-fed babies, symptoms often appear when formula is first introduced. In breastfed babies, cow's milk proteins from the mother's diet can pass into breast milk and trigger reactions. Key signs include persistent reflux, colic, eczema, blood in stools, and faltering growth.

When to seek specialist assessment

• Your baby has had an immediate reaction (hives, swelling, vomiting) after eating
• Your baby has persistent reflux, colic, or loose stools not responding to treatment
• There is blood or mucus in your baby's stools
• Your baby has eczema that is difficult to control
• Your baby has faltering growth or poor weight gain
• You are concerned about introducing allergenic foods
• Your baby has a family history of food allergy, eczema, or asthma

What happens at a specialist assessment

Dr Anandarajan will take a detailed history of your baby's symptoms, feeding history, and family background. Depending on the clinical picture, skin prick testing and/or specific IgE blood tests may be recommended. For suspected non-IgE-mediated allergy, a supervised elimination and reintroduction protocol may be used. You will leave with a clear diagnosis, a written management plan, and guidance on safe feeding.