Cows milk protein allergy (CMPA), also known as cows milk allergy (CMA), is one of the most common food allergies in babies and usually appears before the age of one. CMPA occurs when a babys immune system reacts to the proteins found in cows milk, causing allergic symptoms. Milk allergy results from an immediate allergic reaction in individuals sensitized to the proteins casein, B-lactalbumin, and B-lactoglobulin.