Milk protein may produce immune-mediated hypersensitivity reactions that are seen as skin, gastrointestinal and/or respiratory symptoms. This is called milk allergy or hypersensitivity. It is thought to be a disease of infants but recent studies have suggested that it may be common also in adults. In this paper, the participation of all of the four types of hypersensitivity reaction in milk hypersensitivity is surveyed and the role of antibodies and phagocytic is discussed. Also, the role of probiotics in alleviating milk hypersensitivity is reviewed.