You’re more microbe than human – if you count all the cells in your body, only 43% are human

■ The rest is our microbiome and includes bacteria, viruses, fungi and single-celled archaea

■ The human genome – the full set of genetic instructions for a human being – is made up of 20,000 instructions called genes

■ But add all the genes in our microbiome together and the figure comes out at between two million and 20 million microbial genes

■ It’s known as the second genome and is linked to diseases including allergy, obesity, inflammatory bowel disease, Parkinson’s, whether cancer drugs work and even depression and autism