Maybe we should launder our money.

Hard currency is literally crawling with crap — as in, actual fecal matter, bacteria, pet DNA, and even cocaine — according to several studies that will make you go cashless if you haven’t already.

The latest report swabbed $1 bills circulating around New York City, and found more than 100 different strains of bacteria from our skin and our mouths on the dirty dollars.

So what makes this money so gross? Well, our cash is made from a blend of cotton and linen, and these fibrous crevices are great places for bacteria to grow. Paper-based money can transfer live flu viruses for up to 17 days, and we rarely think to wash our hands before or after handling money. That’s one reason why countries like Canada and the U.K. switched to plastic-based banknotes in 2013 and 2016, respectively: They carry less bacteria, and you can wipe them clean.

“Bacteria can live for weeks on bills, especially considered where they’re kept: rolled up in a pants pocket, or folded into a wallet or purse, and sequestered in a nice, warm dark place where bacteria likes to grow,” Dr. Philip Tierno, a clinical professor of Microbiology and Pathology at NYU School of  Medicine, told Moneyish.

And the longer that money stays in circulation, the more it comes into contact with human hands carrying all sorts nasty substances. Lower denominations like singles and fives have a shorter lifespan (between five and six years, according to the Federal Reserve) because they come into contact with so many people. One calculation suggests $1 and $5 bills get exchanged 110 times a year. But $100 bills, while traded less frequently, can circulate for 15 years, which also exposes them to all kinds of contaminants over time. A U.K. study even found that more than 2,000 people will handle a 20 pound note over nine years. And bacteria feed off of the skin and oil residue our hands leave on bills.

“Wash your hands after handling money, and before you touch your face, your mouth, your eyes and your nose, or any abrasions on your skin, or before eating and drinking,” suggested Dr. Tierno. “The idea is to remember it’s dirty. You wouldn’t put money in your mouth, so don’t put your hands near your mouth after touching it.”

Here’s five of the scariest substances that scientists have found on your money.

  • Cocaine. Yes, you’ve probably handled drug money. Traces of cocaine can be found on 80% of dollar bills, which have been laced by people rolling up the bills to snort the drug, or from money and coke changing hands during drug deals. And traces of morphine, heroin, methamphetamine and amphetamine have also been found on bills, although not as commonly as cocaine.
  • Poop. A 2002 report in the Southern Medical Journal reported that paper money can carry more germs than a household toilet. A whopping 94% of dollar bills tested contained harmful pathogens like staphylococcus – the bacteria that causes staph infections, and can be passed by not washing your hands after using the restroom, or from contaminated food and dairy products.
  • Acne agents. Apart from staff infections, the petri dish that passes for your cash also carries acne-causing bacteria in abundance, as well as microbes linked to pneumonia, food poisoning and gastric ulcers, with even some traces of antibiotic-resistant MRSA (Methicillin-resistant Staphylococcus aureus) bacteria.
  • Dog spit. The NYC study that found more than 100 different strains of bacteria on dollar bills also found traces of DNA from unspecified domestic animals. A previous NYU study, however, found trace DNA from animals including dogs and, surprisingly, horses.
  • Food. Food particles have been found on money and on ATM keypads as we eat and then take out money to pay for our grub. In fact, these traces could be used to track human behavior, as a 2016 study of NYC ATMs found that Harlem residents left more domestic chicken traces on ATMs than those in Flushing and Chinatown, who left more traces of bony fish and mollusks. But this can also transmit food-borne illnesses like salmonella and E. coli.