10 'Harmless' Things You Should Really Wash Your Hands After Touching

"Here's all that money I owe you. I even threw in some bacteria free of charge." iStockphoto/Thinkstock

Everyone loves a full wallet -- the decadent smell of leather and currency, the pockets bulging with credit cards, the change pouch rattling with coins. If you're lucky enough to carry such riches, you might want to consider the other bounty in your billfold. Research now suggests that your folding money may be a playground for pathogens. One 2002 study conducted in western Ohio found that 94 percent of $1 bills contained disease-causing bacteria [source: Bryner]. Another study in England proved that the problem is universal. Scientists there swabbed the hands, currency and credit cards of 272 people in London, Birmingham and Liverpool, then tested for the presence of fecal bacteria. As you might expect, the subjects' hands were pretty disgusting, but 8 percent of the swabs from the cards and 6 percent of the swabs from the bills had as much fecal bacteria on them as you would find in a dirty toilet bowl [source: Chan].

Coins carry their fair share of germs, as well. African researchers analyzed coin samples taken from a variety of street vendors and other locations in a residential neighborhood in Nairobi [source: Kuria]. They isolated a number of potentially pathogenic bacteria, including E. coli, klebsiella, salmonella and staphylococcus. They also found residue from fungal strains known to cause diseases, leading them to recommend good hand hygiene for anyone handling coins all day long. This is especially important in restaurants, where people who exchange money with customers also prepare food.