They're on the money
A study of what lives on 10 countries’ currencies reveals plenty of germs
By Stephen Ornes
Web edition :Tuesday, January 18th, 2011
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A magnified look at a British pound note shows the note’s fibers, good places where germs could get cozy.Vriesekoop
People in different countries use different types of money: yuan (also known as renminbi) in China, pesos in Mexico, pounds in the United Kingdom. Nigerian businesses use nairas, Dutch and Irish accept euros. In the United States, Australia and New Zealand, people buy things with dollars. In the landlocked African nation of Burkina Faso, the currency is the CFA franc.
They may use different currencies, but these countries, and probably all countries, still have one thing in common: Germs on the banknotes. If you have some paper money in your pocket, get it out. Study it closely. Look for anything unusual. Now wave—because lots of little microbes probably live on your money. They’ll be with you until you get rid of the bill.
Scientists have been studying the germs on money for well over 100 years. At the turn of the 20th century, some researchers began to suspect that germs living on money could spread disease.
Most studies of germy money have looked at the germs on the currency within one country. In a new study, Frank Vriesekoop and other researchers compared the germ populations found on bills of different countries. Vriesekoop is a microbiologist at the University of Ballarat in Australia. He led the study, which compared the germ populations found on money gathered from 10 nations (those listed in the first paragraph.) The scientists studied 1,280 banknotes in total; all came from places where people buy food, like supermarkets, street vendors and cafes, because those businesses often rely on cash.
Overall, the Australian dollars hosted the fewest live bacteria — no more than 10 per square centimeter. A square centimeter is a unit of area that is almost equal to the size of the nail on a child’s index finger. Chinese yuan had the most — about 100 per square centimeter. (Imagine 100 germs on your fingernail!)
Most of the germs on money probably would not cause harm. While six types of currency were germier than the United States dollars, U.S. dollars were the most likely to carry E. coli, a bacterium that usually lives in the intestines of animals (including humans). E. coli is largely responsible for food poisoning: People who eat food contaminated with this germ can get very sick.
What we call “paper money” usually isn’t made from paper. The U.S. dollar, for example, is printed on fabric that is mostly cotton. Different countries may use different materials to print their money. Some of the currencies studied by Vriesekoop and his team, such as the American dollar, were made from cotton. Others were made from polymers. A polymer is made of many molecules linked together like a chain, and can take many forms — it may be a liquid, or a solid, or even act a little like both, like Silly Putty.
The three currencies with the lowest numbers of bacteria were all printed on polymers. They included the Australian dollar, the New Zealand dollar and some Mexican pesos (that country prints some money on polymers and some on cotton).
The other currencies were printed on fabric made mostly of cotton. Fewer germs lived on the polymer notes. This connection suggests that germs have a harder time staying alive on polymer surfaces, the research team concluded. Under the microscope, polymer bills look smoother than the cotton fabric. This smoothness “appears to hinder the adherence of bacteria,” Vriesekoop told Science News. In other words, the bacteria may have a hard time sticking to the smoother surfaces.
Scientists need to do more studies to understand how germs live on money — and whether or not we need to be concerned. Vriesekoop is now starting a study that will compare the amounts of time bacteria can stay alive on different types of bills.
Whatever he finds, the fact remains: Paper money harbors germs. We should wash our hands after touching it; after all, you never know where your money’s been. Or what’s living on it.
POWER WORDS (adapted from the Yahoo! Kids Dictionary)
bacterium A life form that is a single cell and too small to see without using a microscope. Bacteria (plural of bacterium) live in almost every environment on Earth, including very cold places, very warm places, in all types of water, in the air, even on and in plants and animals. These microorganisms can also cause disease in plants and animals.
polymer Any of numerous natural and man-made materials consisting of up to millions of repeated linked units, each a relatively light and simple molecule.
currency Money in any form in actual use for the exchange of goods and services. “Currency” often refers to “paper” money in circulation.
germ A tiny life form or microorganism, especially a pathogen, which is a microorganism that carries or causes disease.
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