Scientists have now finally cracked the case on whether double dipping is a food safety problem, or simply a bad habit.
And it is bad news for naughty dippers, as scooping up a second helping of salsa really does spread germs.
At last the words said to George Costanza during a classic 1993 episode of Seinfeld has some scientific weight behind it. During The Implant
, the character dips a chip during a wake, before a shocked mourner tells him 'That's like putting you whole mouth right in the dip!"
Now Harvard University's Healthbeat
journal has reviewed the evidence and warns that double dipping does spread germs.
Dr Robert Shmerling, its editor, describes a study in the Journal of Food Safety
, showing how bacterial counts in dips surged after a person took a bite from a crisp and then dipped again. The number of bacteria also varied with the dip. For example, salsa accumulated more germs than chocolate or cheese.
Another study looked at the threat from popcorn shared by groups with people putting a handful into their mouth then putting the same saliva-contaminated hand back into the popcorn.
The paper, in Food and Nutrition Sciences
, said saliva contained 1m bacteria per millilitre. "About 700 bacterial species are found in the mouth and ... most are considered pathogenic [capable of causing disease]."
Shmerling said the least irresponsible action was for double dippers to at least turn their crisp or cracker around so only the unbitten end enters the dip.
"This research does raise the possibility that a person who is sick might spread a disease by re-dipping a chip [crisp]." Pneumonic plague, TB and Legionnaires' disease all spread via saliva.