Washington, Aug 17 - You may be carrying a whiff of cocaine in your wallet, purse or pocket if you have US bank notes.

In what researchers describe as the largest, most comprehensive analysis to date of cocaine contamination in bank notes, scientists are reporting that cocaine is present in up to 90 percent of US bank notes.

The scientists found traces of cocaine in 95 percent of the bank notes analysed from Washington D.C. alone.

Scientists tested bank notes from more than 30 cities in five countries, including the US, Canada, Brazil, China, and Japan, and found 'alarming' evidence of cocaine use in many areas.

The US and Canada had the highest levels, with an average contamination rate of between 85 and 90 percent, while China and Japan had the lowest, between 12 and 20 percent contamination.

The study is the first report about cocaine contamination in Chinese and Japanese currencies.

Scientists have known for years that paper money can become contaminated with cocaine during drug deals and directly through drug use such as snorting cocaine through rolled bills.