Lactose intolerance is a common gastrointestinal condition caused by the inability to digest and absorb dietary lactose. Primary lactose intolerance is the most common type of lactose intolerance. It is one of the most common forms of food intolerance and occurs when lactase activity is reduced in the brush border of the small bowel mucosa. People may be lactose intolerant to varying degrees, depending on the severity of these symptoms. When lactose is not digested, it is fermented by gut microbiota, leading to abdominal pain, bloating, flatulence, and diarrhea with a considerable intraindividual and interindividual variability in the severity of clinical manifestations. These gastrointestinal symptoms are similar to cow's milk allergy and could be wrongly labeled as symptoms of "milk allergy." There are important differences between lactose intolerance and cow's milk allergy. Therefore, a better knowledge of these differences could limit misunderstandings in the diagnostic approach and in the management of these conditions. [Pediatr Ann. 2021;50(4):e178-e185.].