We leave traces of bacteria on everything we touch—SkyMall catalogs, elevator buttons, the office coffee pot—but physical contact isn’t the only way to make a microbial mark. Humans unknowingly shed swarms of bacteria that linger in the space around them, creating a “microbial cloud.” Now, new research published online today in PeerJ, reveals that the clouds of airborne bacteria may be entirely unique to each person, like a microbial fingerprint. To reach this conclusion, the scientists ran two experiments in which they placed participants in a sanitized room and surrounded them with rings of petri dishes and suspended air filters to catch floating microbes. They compared the captured samples with the microbes of a humanless, but otherwise identical room, and showed that the two spaces were microbially distinct. This provoked another question: If a person’s microbial cloud can set two rooms apart, can it set two people apart? For six of the eight participants, the answer was yes. The researchers sequenced the microbial cloud samples and saw that many of the participants had the same bacteria in their clouds, but in different concentrations. Although they’re not entirely sure how far an individual’s microbial fog extends, the team estimates that our microbes float within a 90 centimeter radius—meaning that in any semicrowded space (a subway, grocery store lines, or the morning meeting at your office) there’s a high chance our microbes are mingling, as shown in the image above. Researchers speculate that when microbes mix, humans may take bacterial souvenirs from one another, a potential contributor to how we develop our individual microbiomes.