CMPA is a hypersensitivity reaction that is initiated by specific immunological reactions to the ingestion of cows’ milk. This can occur at any time from birth,³ and almost all cases present before 12 months of age.⁴

In approximately 70 per cent of CMPA cases, the immune pathology is unclear, non-immunoglobulin E (non-IgE). However, around 30 per cent of cases result from the antigen (allergen), milk proteins, binding to immunoglobulin E (IgE), which in turn induces an immune response.²

IgE-mediated symptoms generally arise within one hour of cows’ milk ingestion, whereas non-IgE-mediated reactions are typically delayed, occurring from one hour to several days after cows’ milk ingestion.^3,4 This could make diagnosing CMPA more difficult, so if a baby presents with any symptoms that suggest CMPA, refer them to the GP as soon as possible.