Cows' Milk Protein Allergy

What it is, and what it is not

NICE defines cows' milk allergy as "a reproducible immune-mediated allergic response to one or more proteins in cow's milk". The immune system is the operative part. That is what separates it from lactose intolerance, which is a digestive problem with an enzyme and cannot cause anaphylaxis.

NICE describes it as one of the most common presentations of food allergy in early childhood, and notes that "almost all cases present before one year of age".

Two mechanisms, two clocks

IgE-mediated

These are the immediate reactions. NICE puts the window at typically up to two hours after ingestion, and lists typical symptoms as urticaria, angio-oedema, itch, cough, hoarseness, wheeze or breathlessness. Multiple systems can be involved at once. NICE says IgE-mediated allergy should be suspected particularly when symptoms are multiple, persistent, severe or treatment-resistant.

Non-IgE-mediated

These are the delayed reactions, and they are the ones that get missed for months. NICE gives the window as between two and seventy-two hours after ingestion, and lists gastro-oesophageal reflux disease, abdominal discomfort, constipation, diarrhoea or atopic eczema, "particularly if symptoms are treatment-resistant". The word treatment-resistant is doing a lot of work: eczema that will not settle on the usual creams, or reflux that does not respond to feeding changes, is the pattern that should prompt the question.

Mixed IgE and non-IgE reactions also occur. The two clocks are the reason a food diary is worth keeping: an immediate reaction is easy to attribute, a reaction three days later is not.

How it gets diagnosed

NICE describes an assessment that covers symptoms, their timing in relation to milk exposure, how reproducible they are, any other atopic conditions, nutritional status and growth. Where IgE-mediated allergy is suspected, that leads to skin prick testing or serum-specific IgE testing, arranged through a specialist allergy clinic where appropriate.

Where non-IgE-mediated allergy is suspected and specialist referral is not needed, NICE sets out a specific sequence: a trial elimination of all cows' milk from the mother's or infant's diet for two to four weeks, followed by home reintroduction to confirm the diagnosis if symptoms clearly improved.

That reintroduction step is not optional and it is the step most often skipped. Without it, a child can end up on a restricted diet for years on the strength of a coincidence. NICE lists restricted diet and malnutrition among the complications of the condition, alongside parental stress and reduced quality of life.

What to feed instead

If cows' milk allergy is diagnosed, a GP will prescribe a hypoallergenic infant formula with fully hydrolysed proteins, which the AAP describes as predigested. Several widely available products are not substitutes for this, and the distinctions matter:

• Comfort formula is partially hydrolysed. The NHS states it is not suitable for babies who have cows' milk allergy.
• Goats' milk formula is not an allergy formula. The NHS says it "is not less likely to cause allergies in babies than cows' milk formula", and is not suitable for infants with cows' milk allergy because the proteins are very similar. The AAP says the same, citing high rates of cross-reactivity with cows' milk proteins.
• Soya formula is occasionally used as an alternative but only from six months and only under medical supervision.
• Plant drinks such as oat, almond or coconut are not infant formula and cannot replace it in the first year.

The NHS asks you to talk to your GP before using any hypoallergenic or soya-based formula, and notes that a product labelled hypoallergenic is not automatically suitable for a diagnosed cows' milk allergy.

If you are breastfeeding

Cows' milk protein passes into breast milk, which is why NICE frames the elimination trial as covering "the mother's/infant's diet". A parent excluding all dairy needs a plan for calcium and vitamin D, which is one of the reasons NICE recommends considering referral to a paediatric dietitian, both to monitor growth and nutrition and to advise on hypoallergenic infant formulas.

Reading labels

Milk hides under many names. The AAP's list of label words that mean milk is present includes milk, whey, curds, milk by-products, dry milk solids and nonfat dry milk powder. UK and Irish allergen labelling law requires milk to be emphasised in the ingredients list of prepacked food, which makes scanning faster once you know what you are looking for.

The milk ladder, and how long it lasts

Where non-IgE-mediated allergy is confirmed, NICE advises a cows' milk-free diet for the mother or infant "until the child is 9–12 months old and for at least 6 months". After that, and if there are no contraindications, a home reintroduction is used to see whether tolerance has developed, following a structured milk ladder that starts with milk baked into food and works up towards fresh milk.

The outlook is reasonable. NICE notes that non-IgE-mediated allergy is generally associated with a faster rate of resolution than IgE-mediated allergy. Many children outgrow it.

Weaning with cows' milk allergy

Weaning still starts at around six months, and the current allergen advice still applies to the other common allergens. NICE lists significant atopic eczema with multiple or cross-reactive food allergies as a reason to consider specialist referral, so a baby with confirmed cows' milk allergy plus severe eczema should be introducing other allergens with advice rather than alone.

When to get help urgently

NICE instructs immediate ambulance transfer for systemic symptoms or suspected anaphylaxis, with or without angio-oedema. Call 999 for sudden swelling of the lips, mouth, throat or tongue, breathing difficulty or wheeze, a tight throat or trouble swallowing, skin turning blue, grey or pale, sudden confusion or drowsiness, or a baby who is limp, floppy or not responding normally.

See a GP without delay for faltering growth, blood or mucus in the stools, persistent vomiting or diarrhoea, or eczema and reflux that are not responding to standard treatment.