Symbiotic bacteria act as a barrier to pathogenic bacteria and promotes the development of the host's immune system in the gut and the skin in a number of ways; These includes; they prevent growth of harmful pathogens by altering the pH, consuming nutrients for pathogen survival, secreting toxins that inhibit the growth of pathogens. Additionally,some may release ant-inflammatory products, other commensals promote the development of B cells that produce protective antibody (IgA), others trigger development of isolated lymphoid follicles in the intestines.