Question: How much bacteria do we need to live? What percentage of bacteria is good for us?

Jane Charlesworth answered on 19 Mar 2014:

Our bodies are made up of about 10 times as many bacteria as human cells. But bacteria are much smaller than human cells, so that works out at about 3% of our body mass being bacteria. Most of these bacteria live in the gut, where they help us digest food.

We don’t know for sure how many different kinds of bacteria live on a human, but the estimate is around 1000 species. This can vary between different people, though– people have different bacteria on their right and left hands and dogs and owners share more bacteria than people in the same family.