We critically revisit the ″common knowledge″ that bacteria outnumber human cells by a ratio of at least 10:1 in the human body. We found the total number of bacteria in the ″reference man″ to be 3.9·1013, with an uncertainty (SEM) of 25%, and a variation over the population (CV) of 52%. For human cells we identify the dominant role of the hematopoietic lineage to the total count of body cells (≈90%), and revise past estimates to reach a total of 3.0·1013 human cells in the 70 kg ″reference man″ with 2% uncertainty and 14% CV. Our analysis updates the widely-cited 10:1 ratio, showing that the number of bacteria in our … Continue reading Ron Sender, Shai Fuchs, Ron Milo