Prepare to be seriously grossed out: A dollar bill can contain at least 3,000 different microbes, according to new research by New York University's Center for Genomics and Systems Biology.
This small study was the initial step in a large project from NYU to categorize all of the microbes in New York City, and study authors hypothesized that paper money might be a common platform for human-bacteria interaction. In the first part of the study, researchers collected 20 $1 bills in both February and July 2013 (because certain microbes may be more prevalent depending on the season). Swab samples were taken on the front and back of the money to see what types of bacteria existed.
They discovered thousands of microbes from the mouth (probably from people licking their fingers while counting), skin (like propionibacterium acnes, which can cause zits) and even some unidentifiable ones that weren't in their databases. But they weren't surprised by the findings: These types of microbes are found everywhere—not just money, says lead investigator Jane Carlton, Ph.D., a professor of biology at NYU. The team also found more microbes linked to pneumonia from the bills sampled in the winter, which may be more prevalent due to cold and flu season.
In the second phase, Carlton and her team tested another 40 $1 bills from September and October 2013 to see if any of the microbes found were viable and could potentially spread infection. (Translation: How worried should we be?) Some of the bacteria identified in the first stage of the study—like the skin-related ones—could possibly spread contagious diseases, but further research is needed to determine whether or not you should be concerned.
But don't let these findings freak you out too much. Carlton insists that you don't need to be worried about the paper in your wallet. This work just opens up the discussion for health departments to analyze currency as another mode of transferring diseases. Still, Carlton suggests that you wash your hands after handling money the same way you would after using the restroom. Because really, you don't know where that dollar has been.