They camp out on skin, hide between teeth, dwell in stomachs, and make us all stink. Meet your microbiome: the bacteria, fungi, and viruses that inhabit Planet You. Up to 50 trillion tiny beings occupy the average body—outnumbering the 30 trillion or so indigenous human cells in and on your person. And just like flora and fauna have divvied up Earth, different microbial groups inhabit various regions of our bodies. From topknot to toenail, they form entire ecosystems that keep their world (that’s us) healthy, or make it terribly sick. Here are some of the groups we host, from noble knights to villainous scum.
1. Snowy Scalp
Up north, a wild clan of fungi sometimes makes a living in the snowy tresses on your head. Malassezia eat the oils on your scalp, then spit out something called oleic acid. It can dry out your skin, creating a dandruff blizzard.