Lactose intolerance (LI) is considered the clinical syndrome caused by lactose malabsorption (LM). It is possible to identify four causes of lactase deficiency defining four different types of LM: primary (genetic), secondary (acquired), congenital (alactasia), and developmental (in premature infants, so reversible). The aim of this protocol is to investigate through an anonymous online survey the knowledge of the Italian population on clinical, pathophysiological, diagnostic and therapeutic issues of lactose intolerance. Data collected will be divulgated through a publication for both people with IL and nutritionists, enriched with tables and flow charts, to improve the knowledge on lactose intolerance and to support people suffering from this condition. The results of this survey will guide subjects suspected of suffering from lactose intolerance towards a correct diagnosis and a better management.