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 are stirred up from the floor, where they were 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.