The term "dirty money" is for real, as around 90 percent of the US one dollar bills are tainted by cocaine.

A 2009 study by American Chemical Society, where scientists tested banknotes from more than 30 cities in five different countries including the US, Canada, Japan, China, and Brazil, revealed "alarming" usage of cocaine in most areas.

The US had the highest level of contamination at 90 percent and was closely followed by Canada at 85 percent. Meanwhile, China and Japan had the lowest contamination rate at 12 percent and 20 percent, respectively.

Traces of other drugs such as heroin, morphine, methamphetamine were also found of dollar bills, albeit not as commonly as cocaine.

However, this does not necessarily mean that every dollar bill passes through coke-laden paws of seedy characters. Cocaine in powdered form is extremely fine and can easily transfer from one note to another in ATMs or currency counting machines.

Interestingly, narcotics was not the only thing that was found on a dollar bill...

Another study by the Department of Biology, New York University identified over a hundred different strains of bacteria on the banknotes.

One of the most common microorganisms found was Propionibacterium acnes, a bacteria known to cause acne and Streptococcus oralis, a bacteria which is commonly found in mouths.

Other things such as food, DNA from pets and faeces was also found of dollar bills.