“Humans have more bacteria cells than human cells in their body”

It has long been a widely accepted notion that our bodies are overwhelmingly outnumbered by bacterial cells, with a common figure suggesting a tenfold advantage for our microbial inhabitants. This idea has permeated popular science and educational materials for decades, leading many to believe that we are more microbe than human. The simplicity and striking nature of the 10:1 ratio made it easy to remember and share, contributing significantly to its widespread adoption.

The origin of this specific 10:1 ratio can be traced back to early estimates in the scientific community, which, while groundbreaking for their time, were based on more limited data and different methodologies. These initial calculations, often focusing on easily quantifiable areas like the gut, provided a general sense of bacterial abundance. As these figures were published and cited, they became ingrained in the collective understanding of human biology, solidifying the idea that bacteria vastly outnumber our own cells.

However, scientific understanding is always evolving. A significant re-evaluation published in 2016 by researchers from Israel and Canada meticulously re-calculated the numbers using advanced techniques and a more comprehensive approach. This study provided a revised estimate, suggesting that the ratio is closer to 1.3 bacterial cells for every human cell. While bacteria still slightly outnumber our cells, the difference is far less dramatic than previously thought. The numbers are so close, in fact, that factors like a recent bowel movement can temporarily shift the balance, allowing human cells to briefly hold the numerical advantage. This updated scientific evidence highlights the dynamic and complex relationship we share with our microscopic residents.