There were about 39 trillion bacterial cells in the body. About 84% of which are red blood cells, to be about 30 trillion human cells in the body.
There are about 10 times as many microbial cells in the human body as there are human cells.
Humans are colonized by many microorganisms. The average human body is inhabited by ten times as many non-human cells as human cells.
Because of their small size, however, microorganisms make up only about 1 to 3 percent of the body’s mass (in a 200-pound adult, that’s 2 to 9 pounds of bacteria), but play a vital role in human health.
Though they do make up about half of our body’s waste.
Most bacteria won’t hurt you – less than 1 percent of the different types make people sick. Many are helpful. Some bacteria help to digest food, destroy disease-causing cells, and give the body needed vitamins.
Certain microorganisms perform tasks that are known to be useful to the human host but the role of most of them is not well understood.
Those that are expected to be present, and that under normal circumstances do not cause disease, are sometimes deemed normal flora or normal microbiota.