The Epithelial Barrier Hypothesis proposes that environmental exposure to toxic substances affects the epithelial cells and leads to the development of leaky epithelial barriers, microbial dysbiosis, translocation of bacteria to inter- and sub-epithelial areas, and tissue microinflammation, and immune response to opportunistic pathogens and commensals. It also points out a possible link between barrier disruption and inflammation at distant organs, such as joints and central nervous system, due to migration of activated immune cells to target organs.