Microbiota promote homeostasis directly through metabolites and bacterial products, which influence both the epithelial and immune cell response. In addition, dysregulated immune-host interaction favours the development of dysbiosis, which contributes to carcinogenesis through metabolic activities and activation of immune responses. Some protective microbiota (SCFAs) may promote cellular proliferation of cancer-initiated cells (dashed arrow). Brackets contain example compounds. PSA, polysaccharide A; TGF-β, transforming growth factor-β. Stars indicate DNA damage.