You won't believe some of the nasty substances that have been discovered on our banknotes and coins. As some businesses turn to cashless payments to minimise the risk of infection during the coronavirus pandemic we take a look at what can linger on cash, from cocaine to diseases. Click or scroll through to find out about the dirt on your cash.

A 2012 study found that polymer banknotes may provide the perfect breeding ground for scary superbugs such as MRSA and vancomycin-resistant enterococci (VRE). The superbugs survived for a worryingly long time on these banknotes. But while polymer bills can harbor dangerous superbugs, generally plastic banknotes are three times more hygienic than regular cotton or linen-based 'paper' bills and home to fewer bacterial colonies overall, according to a study by Harper Adams University in the UK. Not only that, but they are more easily cleaned and disinfected as they are less likely to be damaged by those processes. More than 50 countries use polymer bank notes, including Australia which first introduced the polymer notes in 1988, New Zealand, the UK which started to transition its money in 2016, and Canada, among others.

Research has shown that most paper money is contaminated with cocaine. Test results suggest pretty much all UK notes acquire traces of cocaine within weeks of entering circulation, while in Ireland every single euro note tested in a recent study showed some trace of the drug. Meanwhile 90% of US bills carry traces of the substance. However, cocaine is less likely to attach itself to the polymer notes that are used in more than 50 countries, which are less porous than paper notes and less likely to carry bacteria and other substances. 

A 2001 study published in Forensic Science International of 10 randomly-selected dollar bills from five US cities found that seven of the notes had been contaminated with heroin. If the test results are truly representative, as many as 70% of US banknotes in circulation could be tainted with the drug. However, it's worth bearing in mind that this study was undertaken almost 20 years ago and only used a small sample size.

The sulphates in crystal meth eat away at banknotes, causing them to disintegrate. When thousands of German euro notes crumbled after being withdrawn from ATMs back in 2006, methamphetamine was found to be the culprit.

Money can make you sick. A 2014 review of relevant studies concluded that banknotes, and to a lesser extent coins, have the potential to transmit harmful pathogens, especially if handled along with food.

Guaranteed to gross you out the next time you reach in your wallet for a note – one in seven English banknotes and a similar proportion of US dollar and euro notes contain traces of faecal matter. Yet polymer notes might not necessarily be safer on this front, as researchers at London Metropolitan University found that bacteria found in faeces was present in cash swabbed in a 2018 study, which included 36 samples from all denominations of coins and notes.

While English banknotes have higher microbial loads, much of the bacteria and viruses on the notes are completely harmless. The Romanian Leu, on the other hand, has the highest prevalence of potentially dangerous pathogens per banknote, according to scientific studies. However, the country has been using polymer banknotes for certain denominations since 1999.

You'd be hard-pressed not to handle a US dollar bill that wasn't teeming with microbes. Tests have shown that as many as 94% of dollar bills in circulation are contaminated with high levels of bacteria.

The average dollar bill is a veritable germ salad. A recent study using state-of-the-art sequencing techniques discovered as many as 3,000 different types of bacteria residing on US notes. Although most were found to be harmless, pathogens showed up in the tests too.

Study after study has shown that the five dollar bill is the filthiest US banknote. These notes are used almost as frequently as lower denominational notes such as the $1 bill but remain in circulation longer, hence the build-up of dirt and germs.

A 2013 study from the University of Oxford found that the average European banknote contains 26,000 bacterial colonies, including virulent strains such as E.coli and salmonella that can cause acute food poisoning. The Danish Krone was the dirtiest note of all with 40,266 bacteria per note, followed by Swedish cash which had 39,600 bacteria per note.

Similarly, in several key studies US dollar banknotes have tested positive for staphylococcus aureus, a potentially dangerous pathogenic bacterium that can cause serious food poisoning in susceptible individuals.

Got a bad case of the flu? The banknotes in your wallet could be to blame. A team in Switzerland found that human influenza virus can survive on banknotes and remain infectious for up to 17 days.

After some confusion, the World Health Organization clarified in early March that it had not issued a statement saying banknotes were spreading coronavirus, despite claims in the media. Coins are thought to be more likely to spread the disease than banknotes although not enough is known about the spread of the virus to suggest how long it remains on certain surfaces. Regardless, during the pandemic many shops that have been open, and the ones that are set to open as lockdowns ease, only accept card payment in order to reduce contact between humans when handing over payment. Better safe than sorry.

Norovirus, aka the winter vomiting bug, is environmentally stable and tough as nails – the virus can survive everything from freezing to being doused in disinfectant and, as might be expected, can survive and remain infectious for up to two weeks on a banknote.

In 2012, researchers conducting a study of international currencies observed that US and Canadian notes are particularly favourable environments for methicillin-resistant staphylococcus aureus (MRSA), and may provide a mode of transmission for the bacteria.

Scientists at New York University have detected traces of anthrax on US banknotes. However, there's no need to panic just yet. The bacterium was present in such small quantities, it didn't pose any risk to health.

Cocaine and other drug users who share banknotes to consume their drug of choice could be putting themselves at risk of contracting hepatitis-C. "Sharing banknotes or straws is a significant risk factor that people need to be more aware of,” warns Professor Graham Foster, of St Mary's Hospital, London.

During the 2014-2016 ebola outbreak in West Africa, researchers indicated that banknotes may help facilitate the spread of the disease, particularly in hospitals. In a related study, the virus was found to remain infectious for up to 30 days on banknotes contaminated with ebola-infected blood.

Although currency can potentially act as a vector for a number of serious life-changing illnesses, HIV isn't one of them. In fact, the chances of acquiring HIV from a banknote or coin are non-existent.

Paper banknotes and coins may turn mouldy in damp conditions and, while unlikely, the fungal spores produced by the moulds may pose a health risk for people with mold allergies or impaired lung function.

Howver, coins contain antibacterial and antiviral metals such as copper and, as a result, tend to carry far fewer bacteria and viruses than banknotes, which thrive on the textile material many notes are made from.

In terms of microbial load, coins are much cleaner than banknotes. A typical coin may harbor up to 1,000 bacteria, while a note might contain several million germs, according to a study conducted by scientists in the Netherlands.

An influential study carried out by US researchers in 1972 found that 13% of the randomly selected coins tested carried potentially pathogenic bacteria and viruses, including staph and proteus bacteria.

Likewise, research has shown that the average £1 coin in circulation harbors more bacteria and viruses, both harmless and potentially harmful, than a regularly-cleaned toilet seat.

So how to you protect yourself from dirty cash? Try to remember to wash your hands, give them a swift swipe over with a wet wipe or rub with some hand sanitiser after you handle money. You'll slash your chances of getting ill if the notes or coins are contaminated with nasties.

Now read: The medical companies racing to find a COVID-19 vaccine