Insides each of us, there are trillions of microbes.
These bacteria, fungi and viruses are on our hands, and face and in our gut.
In fact human cells make up only half our bodies and microbes make up the other half. Instead of being harmful, they help keep us healthy.
Science writer Ed Yong explains the vital role of these immigrant microbes and the unique ecosystem in our bodies in his new book I Contain Multitudes: The Microbes Within Us and a Grander View of Life