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All money, it turns out, could stand to be laundered: the stuff is filthy. Studies show that a solid majority of U.S. bills are contaminated by cocaine. Drug traffickers often use coke-sullied hands to move cash, and many users roll bills into sniffing straws; the brushes and rollers in ATMs may distribute the nose candy through the rest of the money supply. (See the top 10 athlete drug busts.)

Also found on bills: fecal matter. A 2002 report in the Southern Medical Journal showed found pathogens  including staphylococcus  on 94% of dollar bills tested. Paper money can reportedly carry more germs than a household toilet. And bills are a hospitable environment for gross microbes: viruses and bacteria can live on most surfaces for about 48 hours, but paper money can reportedly transport a live flu virus for up to 17 days. It's enough to make you switch to credit.

Read about the science of staying healthy.

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