Trillions of bacteria and other microorganisms live inside of and on the surface of your body. The most concentrated area in your body that houses these microscopic creatures is your colon, or large intestine. Some of these microorganisms promote health and actively protect you against pathogens that lead to illness. These beneficial critters are known as probiotics, which literally means "for life". An overarching goal with digestive health is to have more health-promoting probiotics and fewer pathogenic microorganisms, including parasites, overgrowth of Candida (a yeast), E. coli, and other harmful bacteria.