In a 2017 study by the journal Plos One, researchers analyzed a cross-section of $1 bills from a bank in New York City which alarmingly identified hundreds of different types of microorganisms. Among the most abundant were the microorganism that causes acne, harmless skin bacteria, and DNA from pets.
Germs aren’t the only thing you’ll find on paper money — they’re also frequently carrying small amounts of drugs, which makes sense when you consider the cash-heavy nature of the illicit drug business. Specifically, a study of $1 bills from across the country revealed that 80% had trace quantities of cocaine present.
According to the U.S. Currency Education Program, the average life expectancy of paper money is approximately five years to more than 20 years, depending on the denomination. With such a long lifespan, cleaning currency using chemicals and/or high temperatures is something that’s been investigated by scientists, as was switching to a plastic polymer material, which has proven cleaner in other countries like Canada and Australia. Ultimately, the risk wasn’t great enough to warrant the expense and hassle of taking action, especially considering how dirty other everyday surfaces are, such as handrails.