A milk allergy is an immune system reaction that occurs when the body mistakenly identifies proteins in cow's milk as harmful. This can lead to various symptoms, including hives, stomach pain, and difficulty breathing. It is most common in infants and young children, but some may outgrow it as they age. Unlike lactose intolerance, which involves difficulty digesting lactose, a sugar in milk, a milk allergy can cause severe reactions. Treatment typically involves avoiding all sources of milk and dairy products. In some cases, individuals may need to carry an epinephrine auto-injector for emergency situations.