In a baby with CMA, their immune system mistakenly identifies a protein in cow's milk as harmful and triggers an allergic reaction. This leads to symptoms that can either occur immediately (within minutes or up to a few hours) after consuming a food containing cow's milk protein or taking a few hours or up to a few days to develop. Symptoms vary but there may be skin problems (such as an itchy rash or eczema), digestive problems (such as tummy pain, frequent poos that may contain blood or mucus, or constipation), hay-fever like symptoms (such as sneezing or a runny nose) or breathing problems (such as coughing or wheezing).

The type of CMA a baby has depends on how the immune system reacts to the cow’s milk protein. CMA may be IgE-mediated, non-IgE-mediated or a mixture of both. The different types of CMA are associated with different timings of symptom onset. The symptoms themselves may differ for the different types but many overlap. Read more about this on the different types of CMA page.

CMA is often confused with colic or lactose intolerance, but these are not the same. Find out about the differences on the CMA and colic and CMA or lactose intolerance pages.

CMA is the most common food allergy in under 3 year olds. It affects between 2% and 7.5% of all babies, both breast-fed and formula-fed. The good news is that more than three-quarters of babies with CMA grow out of it in early childhood and can return to a normal diet.