CMPA is quite common and may present as persistent vomiting, diarrhoea / constipation, poor weight gain, dry skin / rash, blood in stool and excessive crying. Treatment is by eliminating cows milk (CMP) from diet but only under specialist supervision.
There are two types, IgE mediated and Non IgE mediated. Basically, the latter usually presents later (4-6 weeks of age) and is milder but there is no test for it. If baby is breast fed, then treatment is eliminating dairy from mum’s diet (I know, it’s not nice, but luckily only for few months).
If formula fed, then there are several extensively hydrolysed formulas available like Aptamil Pepti 1/2, Similac Alimentum, Nutramigen. They are broken down proteins, so taste and smell horrible (Honestly, they have not been able to improve the taste of any of these). Fortunately, babies haven’t developed lots of taste buds, so are usually able to drink these (sometimes takes a lot of perseverance!). Parents can close their noses while making them!
The effect of dairy elimination from maternal diet or change to Hydrolysed formula is not apparent immediately, as CMP takes 2-4 weeks to be eliminated from baby’s body. But slowly symptoms like like reflux, skin, vomiting, irritability, blood in stool start to resolve.
The good news is that most children grow out of Non IgE mediated CMPA (the much more common one) between the age of 1 to 2 years. We recommend challenging them with milk formulas beginning from 6 month onwards by use of a milk ladder:
http://cowsmilkallergyguidelines.co.uk/downloads-and-resources/downloadable-map-milk-ladder/
Many cases are associated with Gastroesophageal Reflux Disease (GORD) and may need treatment for that as well. See GORD at https://wordpress.com/post/ramnikmathur.com/130