CMPA (Cow's Milk Protein Allergy) is an immune system response to the protein in cow's milk, which can cause symptoms like rashes, blood in stool, vomiting, or diarrhea. Lactose intolerance, however, is a digestive issue caused by the body's inability to break down lactose (a sugar in milk), which typically results in bloating, gas, and digestive discomfort. While both cause distress, CMPA is an allergic reaction, whereas lactose intolerance is a temporary or permanent inability to digest dairy sugars.