Microbes in and on our bodies have coevolved with us, with each individual having their own assortment of germs (microbiota). The gut microbiota is the most abundant and well-studied, with bacterial density reaching 1011–1012 cells/g in the distal human colon. The number of bacteria in the human gut is predicted to outweigh somatic cells in the body by an order of magnitude, with the gut microbiota's biomass reaching 1.5 kg. As a result, the gut microbiota can be viewed as a multicellular organ comparable to the liver in size. A healthy person's microbiota will also protect them from harmful organisms that enter the body by drinking or eating polluted water or food. Anti-inflammatory agents, pain-relieving substances, antioxidants, and vitamins, for example, can be produced by members of the gut microbiota to protect and nourish the body. They may also prevent dangerous bacteria from attaching and acting, which can produce toxins that cause chronic disease. Synbiotic bacteria are essentially a human organ because of their intimate and specialised contact with human cells, exchanging nutrients and metabolic wastes.