You are not outnumbered ten to one
Bacterial cells in the body and human cells are in the same order of magnitude. The famous ten-to-one ratio was an overestimate.
Established2 min read
A 1970s back-of-the-envelope figure, that bacteria outnumber our cells ten to one, hardened into a fact by repetition. Sender, Fuchs, and Milo redid the census in 2016. A typical man has on the order of 30 trillion human cells, about 90 percent of them red blood cells, and about 38 trillion bacteria, the great majority of them in the colon.
The ratio is near one, and it moves. It moves a lot with a bowel movement. By mass, human cells dominate, because a human cell is much larger. By gene count, the microbes still win, which is a different and still interesting sentence.
Caveats
- The numbers are for a reference body. They are not a personal lab result.
- 'Bacteria' here are mostly gut residents. Skin, mouth, and the rest are smaller terms in the count.
Sources
- 1Sender R., Fuchs S., Milo R.. Revised estimates for the number of human and bacteria cells in the body. Cell 164, 2016.