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Published: Jan 04, 2017 3 min read

Americans have generally been reluctant to get rid of paper money and fully embrace cashless payment systems like Apple Pay or Venmo.

Proponents of the cash-free lifestyle point out the convenience and efficiency of foregoing wads of bills. But perhaps a better argument is that cash, which is swapped into the hands of countless random people, is gross. Studies show that traces of mold, yeast, bacteria, fecal material, and even heroin and cocaine turn up on cash—bringing new meaning to the term "filthy rich."

"Fecal bacteria and other pathogens may have hitched a ride from someone’s hands, nose or apron onto our cash. And yeast or mold might have taken hold, too," a new Scientific American report explains. "Lower-denomination bills are used more often, so studies suggest our ones, fives and tens are more likely to be teeming with disease-causing bacteria."

The Scientific American article pulls from research conducted over the course of several decades. One 1998 study, for example, looked at dollar bills from cities around the U.S. and found tiny amounts of cocaine on more than half the samples, while another research paper found traces of heroin on a smaller percentage of bills. When you think about it, this makes some sense: Illicit drug deals are generally cash-only transactions, and people often roll up paper money to snort the drugs.

U.S. paper currency, which is manufactured with a blend of cotton and linen, appears to be more likely to attract bacteria and hold it longer than banknotes from countries such as Australia and Canada. And the $1 American bill appears to be the dirtiest dollar of all: In one government study, 94% of $1 bills were harboring bacteria, including some that can cause pneumonia, blood infections, diarrhea, and urinary tract and respiratory system infections. Research has revealed that the flu virus can survive up to 17 days on banknotes when accompanied by mucus, which is doubly disgusting.

All that said, it's unclear how many people actually get sick as a result of handling tainted cash. Surely, most people conduct cash transactions without any noticeable health repercussions. But the reports are enough to send you screaming to the Purell—and perhaps to one of the emerging smartphone payment options too.