I have always tried to refute the notion that double dipping is GROSS and unhealthy, when really, on the MOLECULAR level, I don't see it as any sort of real threat. I'm an artist who also loves science, so I tried to describe it visually. Take in mind that my theory explained here does NOT take into mind the 'commet tail effect' in which case, germs MAY get into the mix more easily. Enjoy!