There is an unexplored planet in our solar system. A strange world of bizarre creatures locked in a fight for survival. This unknown world is the human body. Inside and out, it's teeming with a trillion cells that are not us - but are very much the making of us. Each one of us is a walking ecosystem, crowded with creatures that exploit every niche of our body. 90 per cent of the cells in our body are not of human origin, yet they will determine out health, our life expectancy and even our behaviour. Microbes have changed the course of human history and altered our evolution. Microscopic life forms can poison, paralyse, starve and suffocate us. They can eat our flesh, and bleed us to death. But there are others that keep us alive. The war on our bodies never ceases, yet we never notice it. We are born 100% human, but will die 90% microbial. Between these bookends of our lives is an unexplored world - LIFE ON US