The Science of Double-Dipping: A Health Risk or Just Gross?

Double-dipping a chip sure sounds gross, but can enough germs really be transferred to make you sick? What does science have to say about double dipping?

Sabrina Stierwalt, PhD
4-minute read
Episode #312
dipping a chip in cheese sauce

Around the holidays we tend to like to gather...for holiday parties, family get-togethers, and end-of-the-year work functions. These gatherings often mean delicious food, especially gooey bowls of dip like salsa, ranch, cheese, or my favorite, spinach artichoke. All of this togetherness and shared food, unfortunately, coincides with the middle of flu season. And with every bite of tasty dip, you run the risk of having been preceded by the infamous double-dipper.

The double-dipper is the person who will re-dip their chip (or piece of bread or vegetable stick) back into the communal bowl of dip after having bitten into it, thus transferring their saliva, and any germs that come with it, also back into the bowl. Swapping saliva with a dozen other people at the party who share the same taste in dip as you sure sounds gross, but can enough germs really be transferred via double-dipping to cause someone to get sick? What does science have to say about double-dipping?  

Does Double-Dipping Spread Bacteria?

The most thorough, and often quoted, study on double-dipping in the laboratory was conducted by researchers at Clemson University and published in 2009 under the title “Effect of Biting Before Dipping (Double-Dipping) Chips on the Bacterial Population of the Dipping Solution” in the Journal of Food Safety. The experiment was done in three parts.

First, researchers asked participants to repeatedly dip crackers or chips into sterilized water both before and after biting the chip. They found significantly higher levels of bacteria (1,000 more per milliliter) in the water after double-dipping had occurred. Next, the researchers again used sterilized water as a “dip” but this time they varied the pH or acidity levels of the water. Again, they found more bacteria in the water dip after a chip had been double-dipped. They also found that the more acidic watery dip had lower levels of bacteria—both immediately after double-dipping took place and two hours later, compared to the other, less acidic watery dips.

You’re likely to be more at risk from a sneezing or coughing coworker who is clearly already sick than a potential germ transfer via some rich and creamy ranch dressing.

Finally, participants no longer had to eat chips dipped in water but instead tested salsa (All Natural Tostitos Chunky Hot Salsa, to be precise), chocolate sauce (Genuine Chocolate Flavor Hershey’s Syrup), and cheese (Fritos Mild Cheddar Flavor Cheese Dip). In these cases, researchers found that double-dipping transferred five times more bacteria to the salsa than the other two dips. However, after two hours at room temperature, the bacteria levels in the salsa were back down to levels lower than those in the other dips.

Their experiment thus proves that double-dipping increases the amount of bacteria in the communal dip bowl. How much bacteria depends on the acidity of the dip and how long the dip sits out at the party, with more acidic dips like salsa being more effective at killing off the bacteria more quickly.


About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.

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