Only about 10 percent of the cells in the human body are actually human cells — the rest are fungi, bacteria, viruses or other non-human cells. The human gut alone has over 100 trillion microbial cells, but only about 1 percent of all the microbiota on and in the body has actually been identified. Researchers estimate that the non-human microorganisms in and on a human body outnumber the human cells by a factor of 10.
More facts about non-human cells:
- Although more than 3 million types of microbes are thought to exist, fewer than 8,000 have been described. These microbes make up a full one-third of the Earth's biomass.
- People have unique bacteria signatures. Studies show that people tend to carry about 3,000 bacteria from about 150 species on their hands, but each of a person's hands has different types of bacteria, with an overlap of less than about 15 percent.
- More and more studies have shown that bacteria that were thought to exist only outside the human body actually do exist in the body. For instance, hydrothermal vent eubacteria, a type of bacteria that was once found only near deep sea heat vents, have been found on prosthetic hip joints.