Intestinal permeability is a key aspect of the intestinal barrier, which plays a crucial role in health and disease. The intestinal barrier is a complex structure that separates the internal environment from the luminal environment, and its function is closely linked to the intestinal microbiota and the mucosal immune system. Intestinal permeability refers to the ability of the barrier to allow the passage of molecules between the host and the environment while preventing the entry of harmful substances. The barrier is regulated by various factors, including diet, bacteria, and lifestyle, and its disruption can lead to increased permeability, which is associated with a range of diseases such as inflammatory bowel disease, celiac disease, food allergy, irritable bowel syndrome, obesity, and metabolic disorders. The assessment of intestinal permeability is challenging due to the variability of the barrier function depending on species, genes, diet, and environmental factors. Various methods have been developed to measure intestinal permeability, including the Ussing chamber, permeability assays using markers such as lactulose, mannitol, and PEGs, and the measurement of bacterial products such as LPS and EndoCAb. These methods have limitations, including the invasiveness of some techniques and the lack of correlation between different assays. The intestinal barrier is also influenced by the microbiota, which plays a key role in maintaining barrier function and preventing the translocation of harmful substances. Probiotics and prebiotics have been shown to have beneficial effects on the intestinal barrier by modulating the microbiota and enhancing barrier function. The regulation of intestinal permeability is a complex process involving multiple factors, and understanding these mechanisms is essential for the prevention and treatment of diseases associated with increased intestinal permeability.Intestinal permeability is a key aspect of the intestinal barrier, which plays a crucial role in health and disease. The intestinal barrier is a complex structure that separates the internal environment from the luminal environment, and its function is closely linked to the intestinal microbiota and the mucosal immune system. Intestinal permeability refers to the ability of the barrier to allow the passage of molecules between the host and the environment while preventing the entry of harmful substances. The barrier is regulated by various factors, including diet, bacteria, and lifestyle, and its disruption can lead to increased permeability, which is associated with a range of diseases such as inflammatory bowel disease, celiac disease, food allergy, irritable bowel syndrome, obesity, and metabolic disorders. The assessment of intestinal permeability is challenging due to the variability of the barrier function depending on species, genes, diet, and environmental factors. Various methods have been developed to measure intestinal permeability, including the Ussing chamber, permeability assays using markers such as lactulose, mannitol, and PEGs, and the measurement of bacterial products such as LPS and EndoCAb. These methods have limitations, including the invasiveness of some techniques and the lack of correlation between different assays. The intestinal barrier is also influenced by the microbiota, which plays a key role in maintaining barrier function and preventing the translocation of harmful substances. Probiotics and prebiotics have been shown to have beneficial effects on the intestinal barrier by modulating the microbiota and enhancing barrier function. The regulation of intestinal permeability is a complex process involving multiple factors, and understanding these mechanisms is essential for the prevention and treatment of diseases associated with increased intestinal permeability.