A recent report, published by the American Society of Microbiology in the journal mSystems, indicates that specific cities have their own individual microbial fingerprint. Scientists from Northern Arizona University collected microbial samples in three unique building types in three different North American cities (Flagstaff, San Diego, Toronto) over the course of one year. Their findings revealed that parameters such as building size, ventilation, traffic, humidity and heat had little effect on bacterial make-up between buildings in the same city. However, they found clear differences between cities with each city having a unique diversity and mixture of specific microbial species. Additionally, they found that floors contain the most number of microbes and that a significant, but not majority, amount of the microbes come from human skin.