Lactose is a disaccharide found only in milk, and after weaning, the synthesis of lactase, which breaks down lactose, stops or decreases in most individuals. This condition, known as lactose intolerance, results in the inability of the digestion of milk and is very common in the world. Because of the single nucleotide polymorphisms occurring on the lactase gene, the lactase enzyme can be synthesized for life in some individuals. The prevalence of this condition called lactase persistence varies according to ethnic groups. Although there are various methods for the diagnosis of lactose intolerance, observation of symptoms is often sufficient for the diagnosis of the disease. Those who have lactose intolerance should apply a life-long lactose-free diet. Since milk is a rich source of some important nutrients such as calcium, it is important for lactose intolerance patients to meet their needs like calcium from foods with low lactose content such as cheese and yogurt. In this study, information about lactose intolerance was given and lactose intolerance prevalence, diagnosis methods, and lactose-free diet were examined. This study aims to increase the lactose intolerance awareness of both patients and food industry stakeholders.