In this book, the author takes readers on a safari through the human body, pointing out the long-term residents, the itinerant visitors, the irritating vandals and the ruthless invaders, carefully distinguishing between helpful friends, harmless acquaintances and lethal foes. The book is a journey through our own private biospheres. Along the way, we learn that one-third of the human race is allergic to dust mite faeces; that bad breath is caused by bacteria living on the back of our tongues which release sulphur from the protein we eat; that live maggots are being successfully used to treat drug-resistant infections; that fresh sweat is odourless (the smell results from the activity of armpit bacteria).