Just one person in a room adds 37 million bacteria to the air every hour, according to a study published in the journal Indoor Air.
Most of the bacteria is stirred up from the floor, left behind by the room's prior occupants.
"We live in this microbial soup, and a big ingredient is our own microorganisms," Jordan Peccia, associate professor of environmental engineering at Yale and the principal investigator of the study, said in a press release.
"Mostly people are re-suspending what's been deposited before. The floor dust turns out to be the major source of the bacteria that we breathe."
Not long ago research revealed what lives in your belly button, so the overall amount of bacteria is astounding.