Physical money is remarkably dirty. About 70% of paper banknotes carry more than 3,000 bacterial colonies per bill, and many samples contain so many microbes that lab technicians literally classify them as “too many to count.” Bills picked up from fish markets, butcher shops, and street vendors tend to be the worst offenders, but even currency from cleaner environments harbors a diverse mix of bacteria, fungi, and parasites. The good news: while money is genuinely grimy, the actual risk of getting sick from handling it is low for most people, as long as you wash your hands before eating or touching your face.
What’s Actually Living on Your Cash
A 2024 global systematic review pooling data from dozens of studies found that roughly 30% of banknotes carry coagulase-negative Staphylococcus, a common skin bacterium. About 20% harbor Staphylococcus aureus, the species responsible for staph infections. And nearly 17% test positive for E. coli, a bacterium that comes from fecal matter, which tells you something uncomfortable about the hand-washing habits of the people who touched that bill before you.
The contamination goes well beyond bacteria. Fungi show up frequently, with Aspergillus niger (a common black mold) appearing on about 42% of tested bills, followed by Penicillium species at 26%. Parasites are also present: roughly 19% of sampled currency carried Entamoeba histolytica (which causes amoebic dysentery), about 16% had roundworm eggs, and around 7% tested positive for Giardia. Even hookworm traces turned up in multiple studies at a rate of about 6%.
Several bacteria with genuine disease-causing potential show up regularly. Shigella, which causes severe diarrheal illness, appeared in about 18% of samples across studies. Salmonella turned up in roughly 6%. Klebsiella, a bacterium that can cause pneumonia and urinary tract infections, was found on about 20% of bills tested.
Why Bills Are Dirtier Than Coins
Coins consistently carry far fewer germs than paper bills. In one study of currency from food markets, 76% of coins had fewer than 1,000 bacterial colonies, while 70% of banknotes had more than 3,000. The reason comes down to chemistry and texture.
Copper and nickel, the metals in most coins, are naturally antimicrobial. Free copper ions damage bacterial cell membranes and destroy critical enzymes, killing a wide variety of bacteria (including E. coli and Staph aureus) within minutes to a few hours of contact. Paper bills, by contrast, are made from cotton-linen blends full of tiny fibers that create microscopic hiding places where bacteria can lodge and thrive. Those fibers also absorb moisture, giving microbes a more hospitable environment to survive in.
Paper Bills vs. Polymer Bills
Countries that have switched to polymer (plastic) banknotes, like Australia, Canada, and the UK, may have a slight hygiene advantage. Bacteria survive far shorter on polymer bills than on traditional cotton-based ones. In lab testing, bacterial counts on polymer banknotes dropped by nearly 100,000-fold within the first week, then fell another tenfold in the second week. On cotton-based bills, bacteria hung on much longer.
The difference also shows up in how easily the bills can be cleaned. Bacteria washed off polymer bills almost completely after just 10 rinses, while cotton-based bills retained more than half their bacterial load even after 30 washes. The smooth, slightly water-repellent surface of plastic bills simply gives bacteria less to cling to.
There’s a tradeoff, though. Viruses like SARS-CoV-2 survive longer on plastic surfaces (up to 7 days) than on paper (about 3 hours). So while polymer bills resist bacterial buildup, they may hold onto viruses longer than traditional paper currency.
It’s Not Just Germs
Money also carries chemical contaminants. A well-known analysis of U.S. paper currency found cocaine on 79% of bills tested at detectable levels, with 54% carrying more than 1 microgram. The highest single bill had over 1,300 micrograms. Contamination was found at every site tested, suggesting the drug transfers readily between bills during normal circulation, even onto money that was never directly used for drug-related purposes. The amounts on most bills are far too small to have any pharmacological effect, but the finding illustrates just how efficiently currency picks up and spreads whatever it touches.
How Risky Is Handling Money, Really?
Despite all these findings, health organizations have not recommended avoiding cash. The World Health Organization has stressed hand-washing after handling money, particularly before eating or preparing food, but has not advised banning banknotes or coins. The reason is that the mere presence of bacteria on a surface doesn’t automatically translate to infection. You need a large enough dose of a pathogen to enter your body through your mouth, eyes, nose, or a break in your skin.
For healthy people with intact immune systems, casual handling of money during a normal day poses minimal risk. The danger increases in specific contexts: food service workers who handle cash and then touch food without washing their hands, or people with compromised immune systems who might be more vulnerable to opportunistic fungi like Candida or Aspergillus. Bills from wet markets, butcher shops, and other environments with raw animal products tend to carry significantly higher microbial loads than those from drier settings.
Practical Ways to Stay Clean
The single most effective thing you can do is wash your hands with soap and water for at least 20 seconds after handling cash, especially before eating, cooking, or touching your face. Food safety codes already require food service workers to wash their hands after any activity that could contaminate them, and handling money falls squarely into that category. Hand sanitizer with at least 60% alcohol works as a backup when soap isn’t available, though it’s less effective against certain parasites.
If you handle large volumes of cash for work, keeping hand sanitizer at your station and avoiding touching your face during shifts makes a meaningful difference. And while switching to contactless payment does eliminate this particular exposure, there’s no public health mandate to do so. Money is dirty, but it’s a manageable kind of dirty, the kind that basic hygiene handles well.