How disgusting is double dipping, really? Researchers at Harvard were inspired by the character of George Costanza in a 1993 episode of Seinfeld in which he is caught “double-dipping” a chip at a wake. Double-dipping, for those unaware, is when one dips a chip, takes a bite, and then dips their chip again. The other characters, horrified by George’s behavior, said that his act was akin to putting his entire mouth on the dip.
But does science support George or the other characters in this debate?
To answer the question, the Harvard researchers turn to a 2009 study at Clemson University in which dip is carefully studied before and after someone dips their chips into it. They found:
“Bacterial counts in the dip increased significantly after a person took a bite from a chip and then dipped again.
The number of bacteria contaminating the dip varied depending on the dip – salsa had more bacteria after double-dipping compared with chocolate or cheese dips (perhaps due to differences in thickness and acidity of the dips).” 
They also noted findings that were quite similar when a chip was double dipped in water.
It was also noted that different kinds of dips lead to bacteria traveling at different rates. For example, double-dipping into a shared bowl of salsa might be a more grotesque crime than doing so into a communal bowl of cheese or chocolate. This is largely because salsa is much thicker than cheese or chocolate, and lends itself to the spread of bacteria. 
So does this mean you’ll spread all of your nasty germs to other party goers by double dipping? Harvard’s Healthbeat does say that it can spread illness for sure, especially if the double-dipping offender is sick or is about to get sick. This means you’re better off with your own vat of salsa, or carefully watching others to ensure that they don’t commit the cardinal party sin.
Though not everyone will care so much, especially if the person isn’t clearly sick.
There is one other foolproof solution: turning the chip around and dipping the “back end” of it into the salsa, thus not allowing you to further spread any germs.
 The Independent