What’s the difference between milk allergy and lactose intolerance?

Lactose intolerance is sometimes confused with milk allergy, but the two are quite different. Milk allergy is an immune reaction to a protein in milk, usually casein. Lactose intolerance is not an immune condition. People with lactose intolerance don’t have an immune reaction to lactose; they simply have low or no production of the enzyme which breaks it down, and experience digestive symptoms resulting from the fermentation of lactose by their intestinal bacteria.^[1]