Health visitor Dawn says...
Cow's milk intolerance is an adverse reaction to either the protein component of milk or to lactose - a naturally occurring sugar in cows' milk. Some babies have a shortage of the enzyme lactase, which is made by cells lining the small intestine. Without this they can't break down milk sugar into simpler forms that can be absorbed into the bloodstream.
Symptoms include weight loss or failure to gain weight, being unsettled, persistent crying, reflux, vomiting, colic, burping, bloating, skin rashes, eczema, diarrhoea, constipation and shortness of breath.
Many babies grow out of it by three years, and most will have grown out of it by five. It's essential that tests are done to determine whether his cows' milk intolerance is to the protein or the lactose. If your son is found to be intolerant to the protein, he may still be able to have some cows' milk products. If he's lactose-intolerant, then he may require a low-lactose diet. In either case, get referred to a nutritionist or dietitian, who will recommend a milk formula and diet.