Is money ever clean?

In Hong Kong, the Chinese renminbi was referred to as "dirty money" after a tabloid asked a lab to do an analysis of bacteria-counts on different currencies and banknotes. The renminbi "won", having by far the highest number of bacteria. (On a side-note, Hong Kong now loves the renminbi since they believe it is what makes their wheels go round these days).

But is renminbi really the dirtiest? For the bacteria-phobes out there (Mr Panama, are you reading this?), I present a choice selection of Nepali banknotes. Pictures fail to convey just how incredibly sticky they are! A colleague today told me of an experiment he did: He on purpose left money in his trousers during washing, and was surprised that is some cases the money had become so slippery as to slide out from the pockets. What kind fat/wax/bacteria/dirt/dust-combination will cause that?