The ‘Seinfeld’ Double-Dip Is Exactly as Gross as It Seems, According to Science

Chips and dip make for an easy appetizer at social gatherings: Buy some packaged food and dump it on a plate. But the act of biting into a chip and then dunking it back into the dip, or “double-dipping,” seems like an invitation to spread disease. We don’t walk up and take random bites of food from a person’s hand, so why do we tolerate this?

In an investigative piece for Bon Appétit, writer Ali Francis posed the question to a number of scientists. One of them was Paul Dawson, PhD, who in 2009 authored what may be the definitive study on whether double-dipping is a sanitary practice. The conclusion: It’s disgusting.

Dawson conducted a number of experiments to assess bacterial transfer from a person’s mouth to a communal trough—in this case, a glass of water. An unmolested cracker transferred comparatively few germs when dipped in the water. But a bitten cracker contaminated the water with 1000 more bacteria per milliliter.  

Because we don’t snack on chips and water, Dawson also examined bacterial transfer between bitten and unbitten crackers into a variety of dips, including salsa (Tostitos Extra Chunky, if you’re wondering) and cheese. The dips had no detectable bacteria prior to dipping. After a double-dip, the bacteria increased in number up to five-fold, demonstrating that germs from our mouths use crackers as a highway to the dips.

Whether those germs are going to prove harmful is harder to assess. All mouths contain some bacteria, which may not be an issue. Other times, our mouths will harbor communicable disease, like the common cold, flu, and COVID-19. If someone with problematic bacteria double-dips, it’s certainly possible for other dippers to ingest a scoop of staph with their Tostitos.

Dawson also observed that the kind of dip used matters. Salsa, which is more acidic, is less hospitable to germs. On the other hand, it’s thin enough so that the dip is more likely to run down a cracker and infect the dipping bowl. Thicker dips may not allow bacteria to move around as easily. Someone might double-dip on one corner, leaving the opposite corner of the bowl a somewhat safer option.

So how concerned should you really be? If someone with obvious symptoms of illness is double-dipping, it would be wise to avoid whatever bowl they’re hovering over. Really, they shouldn’t be at a party in the first place. (Though of course asymptomatic people can spread trouble, too.) Otherwise, you can just accept some bacterial transfer is likely and go on with your life. Dips have germs, but so do doorknobs, bathrooms, spice cabinets, and the couch where that one guy keeps sneezing.

Still worried? You can try getting to the dip early, use a spoon to grab some on a plate, and have your own dipping station. Hosts can also consider offering smaller chips or crackers that encourage single-dipping.