Coughs and Sneezes spread diseases/Cover your mouth when coughing.

Buying a pint in a pub in Blackrock yesterday and the female barman coughed all over it while it was resting.....
 
just like plastic bottles and plastic nappies, paper hankies are designed not to break down on contact with liquids.
Not absolutely immediately but pretty quickly - they won't be hanging around for weeks/months, never mind centuries like plastic bottles. As anyone who has ever left a paper hankie in the pocket of black clothing in a washing machine load will attest...