You are carrying around more microbial genes than human ones

The Human Microbiome Project (2007–2016) catalogued the trillions of bacteria, fungi and other microbes living in and on a healthy human body. Their combined genes outnumber our own by roughly two orders of magnitude, and they turn out to shape digestion, immune response and even mood — most of it from organisms we only started seriously counting this century.

— Human Microbiome Project Consortium, A framework for human microbiome research — Nature, 2012