A possible cause of leaky gut is increased intestinal permeability or intestinal hyperpermeability.
That could happen when tight junctions in the gut, which control what passes through the lining of the small intestine, don’t work properly. That could let substances leak into the bloodstream.
People with celiac disease and Crohn’s disease experience this. “Molecules can get across in some cases, such as Crohn’s, but we don’t know all the causes,” Lee says. Whether hyperpermeability is more of a contributing factor or a consequence is unclear.
But why or how this would happen in someone without those conditions is not clear.