The Bacteria In Your Wallet, and Why Dollar Bills Can Be Like a Microbial Playground

Those banknotes in your pocket could be crawling with bacteria.

Although there are those who say we’re increasingly using forms of electronic payment rather than cash, there’s still a heck of a lot of the paper stuff floating around in the US.

In fact, the US Federal Reserve reported that there were no fewer than 38.1 billion banknotes in circulation in 2015.

If you laid these bills end to end, they would reach from here to the moon more than 15 times.

Despite this huge amount of paper currency, I wonder where you stand on the idea of substituting its use with a debit or credit card for hygiene reasons, rather than for mere convenience?

Examining some of the studies that have looked at the bacterial load on banknotes may make you take this more seriously, although of course it’s important to say that just because there are microbes on money, it doesn’t mean they’ll be bad for you.

After all, unless you live in a “clean room” like the ones at NASA, there’s bacteria on just about everything you come into contact with in everyday life.

And actually even clean rooms aren’t always entirely bacteria-free, but that’s another story for another day.

But back to banknotes.

For example, in 2014 New York University’s fittingly-entitled Dirty Money Project subjected eighty $1 bills withdrawn from an unnamed New York bank to the same kind of DNA sequencing we use at uBiome.

The scientists found over 3,000 types of bacteria on them, the most abundant species being one that can cause acne.

The project’s leader suggested that microbes may even thrive on money.

A wallet kept at body temperature may behave like a kind of petri dish.


Incidentally, their study from swabbing just eighty $1 bills generated about 1.2 billion DNA segments, requiring 320 GB of digital storage to hold the genetic data.

Another 2014 study, this one out of King Abdulaziz University in Saudi Arabia, pointed out that retail outlets whose staff handle money and food at the same time can pose a significant public health risk.

They noted that different countries have varying levels of bacteria on their bills.

For example, they found 80% of the banknotes in Bangladesh were contaminated.

The figure was higher at 88% in Saudi Arabia, and 89% in Nigeria.

So how did the US do, then?

Actually, contrary to what you may guess, our banknotes were even dirtier than those of these other countries.

In fact the scientists found bacterial contamination on no less than 94% of US banknotes.

A tiny amount of consolation may come from knowing that dirty money isn’t specific to the United States.

Researchers in the UK in 2012 found that 6% of English banknotes carried levels of E. coli comparable to those found on toilet seats.

In general, the longer a bill stays in circulation, the more opportunities it has to become contaminated, and it’s mainly lower denomination notes that get the most handling as they’re exchanged more often.

It is hand-to-banknote action that largely causes contamination, with banknotes’ surfaces being a great place to harbor bacteria.

In reality, “paper” money is generally around 75% cotton and 25% linen, resulting in a fibrous surface that provides perfect microscopic nooks and crannies for microbes to hide away.

Don’t be fooled into thinking that coins can’t be contaminated, however.

As another part of the study by the Saudi Arabia scientists, it was shown that methicillin-resistant Staphylococcus aureus (MRSA) was able to live on coins in the laboratory for several days.

So what’s the answer?

Well, one solution is to go the way of countries such as Canada, Australia, and New Zealand, who have introduced banknotes made of polymer rather than paper. A side benefit of this is that you can’t rip it.

Since Mexico has a mixture of paper and polymer banknotes, it provides a useful testing ground for comparisons, and sure enough Mexican polymer notes have been found to carry substantially lower levels of contamination than their paper counterparts.

However, since there’s no sign of the US introducing polymer banknotes any time soon, it makes sense to follow the advice of researchers based at the University of Ballarat, Australia in 2010.

In a twist on Indian “eat with your right, wipe with your left” etiquette, they suggest that when retail staff simultaneously handle cash and food, they should use one gloved hand for money, preserving the other for food.

And as for customers, the scientists urged good hand hygiene after handling money and before handling food.

Because it seems that where there are bucks, there are bugs.

Further reading

Bacteria on bank notes

Dirty Money – How Contaminated Is It?

Dirty Money Project

Dirty money: an investigation into the hygiene status of some of the world’s currencies as obtained from food outlets

Money as a Potential Vector of Transmissible Disease

Paper money and coins as potential vectors of transmissible disease

Rob Portman says the national debt in $1 bills would cover all of Ohio

Why You Shouldn’t Put Your Money Where Your Mouth Is