Some 95% of banknotes are covered in harmful bacteria that can cause a variety of serious illnesses, including MRSA, urinary tract infections, pneumonia, and even anthrax.
That is according to a new study by Gambling.com in conjunction with microbiologists, which swabbed 20 of the most-used currencies from around the world. The swabs were used to inoculate agar plates, which were then incubated at room temperature for one week.
The study revealed that the Canadian dollar was the dirtiest and most dangerous banknote in the world, with 209 microbe colonies discovered, spread with the harmful bacillus, a microbe with strains that can cause food poisoning, sepsis, and in rare cases, anthrax.
Watch: Infection risk from handling cash is low, Bank of England concludes
Rhizopus strains were also found on the note, which commonly causes fungal infections.
This was followed by the Brazilian real with 118 microbe colonies, the Hong Kong dollar, which had 42, and the Indian rupee and Filipino peso which both had 14.
The UK pound had seven microbe colonies, with Saccharomyces cerevisiae being the most dangerous. Commonly known as baker's yeast, this microbe bacteria can cause illnesses such as pneumonia and urinary tract infections, as well as infections to the inner lining of the heart and abdomen in the immunosuppressed.
Saccharomyces can cause illness in even healthy humans too, where infection can easily result in thrush.
Cash is known to be covered in germs and bacteria that can lead to the spread of disease. The most common bacteria that were found on banknotes was Saccharomyces cerevisiae, found on 65% of banknotes.
Mucor Racemosus, a rapidly growing, weedy mould was found on 25% of banknotes that were swabbed, while Micrococcus, a type of spherical bacteria, most commonly found on the skin of humans, were discovered on 20% of banknotes.
Micrococcus strains have been reported to cause a variety of infections as opportunistic pathogens. These infections include pneumonia, septic arthritis and endocarditis in the immunocompromised.
Fusarium, also known as michrodochium nivale or 'snow mould', was found on 20% of banknotes and Rhizopus, also known as black mould, a genus of common fungi, was found on 15% of banknote.
Emma Warburton, technical lab assistant in Biotechnology said: “Transmission can occur from contaminated currency – from direct contamination by an infected person, or cross-contamination - where the virus is picked up by high touch areas such as door handles and contaminates the money.
“The person receiving the money could transfer the virus from the contaminated banknote onto their hands. If they don't wash their hands after handling money and touch their face- particularly the nose and mouth, they are at a high risk of infection."
In February last year, China started disinfecting its banknotes to try and stop the transmission of COVID-19. Coronavirus can survive on banknotes for weeks and in the UK, many retailers are encouraging contactless card transactions to discourage people from paying with cash.
Paper notes can be disinfected by exposing them to high heat, such as from an iron. Polymer notes, such as UK banknotes, can be disinfected by cleaning them with antibacterial soap and water with a damp cloth. They should be dried with a cloth afterwards.
According to advice from the World Health Organization (WHO) this is safe to do due to their water-resistant surface.
Experts have warned against disinfecting notes with hazardous materials such as bleach and ethanol, as repeated exposure could damage banknotes and make them unrecognisable and therefore unusable as legal tender.
Watch: Will interest rates stay low forever?