The pharmacy-trained guide to Cow's Milk Protein Allergy (CMPA) in babies — how to tell it apart from lactose intolerance and normal reflux, the clinical signs, and why you need a GP prescription not an OTC switch.
Cow's milk protein allergy and lactose intolerance are not the same thing. Most parents use the terms interchangeably. The distinction matters enormously because the management is completely different, and confusing them can mean a baby suffers unnecessarily for months.
Cow's milk protein allergy (CMPA) is an immune response to the proteins in cow's milk — casein and whey. The immune system identifies them as a threat and reacts. It affects approximately 2–3% of babies.
Lactose intolerance is a digestive issue — the gut does not produce enough lactase to break down lactose, the sugar in milk. True primary lactose intolerance is rare in babies under 12 months. The key difference: CMPA requires removing cow's milk protein entirely.
Immediate reactions: hives, swelling, vomiting, or difficulty breathing within minutes. These require 999 for the first episode.
Delayed reactions are more common and more commonly missed: persistent eczema that does not respond to treatment · reflux that does not improve · blood or mucus in stools · excessive crying after feeds · poor weight gain.
Speak to your GP. Do not remove dairy from a formula-fed baby's diet without medical guidance — the replacement formula must be appropriate for the baby's age and nutritional needs. Your GP may refer to a paediatric dietitian.
For formula-fed babies with confirmed CMPA, the NHS recommends extensively hydrolysed formula (eHF) as first-line — Aptamil Pepti, Nutramigen. Soya formula is not recommended as a first alternative for babies under 6 months. Partially hydrolysed (HA) formula is not appropriate for diagnosed CMPA.
NHS Cow's milk allergy in babies · NICE CG116 Food allergy · BSACI · Reviewed April 2026.