Normal flora / Commensal microbiota
Normal flora
Japanese: 常在菌（常在細菌叢）
Microorganisms that permanently reside on human skin, in the gut, and elsewhere. They form symbiotic relationships with the host and help prevent invasion by external pathogens.
Microorganisms always live on and in our bodies. On the skin, in the mouth, in the gut, in the nasal cavity—bacteria adapted to each location quietly reside there. These are the commensal microbiota.
Commensal bacteria are not merely passive inhabitants. They occupy territory against invading pathogens, serving as a barrier that prevents infection.
The total number of microorganisms living on a human body is said to be roughly equal to the number of human cells themselves. We simply cannot live without this symbiosis with microbes.