Debunking the 10:1 Bacteria Myth: Humans Are Closer to 1:1

A 2016 re-evaluation shows the long-cited 10-to-1 bacteria-to-human-cell ratio is not supported by current evidence. Using updated measurements, the counts are about 3.8×10^13 bacteria and 3.0×10^13 human cells in an average adult, a ratio of roughly 1.3:1 in favor of bacteria. The microbiome remains numerically dominant but not by an order of magnitude; the correction stems from earlier coarse assumptions and a failure to trace the figure to its source. The episode illustrates the value of ordinary scientific due diligence and does not diminish the microbiome’s importance.