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

Does Double-Dipping Spread Disease?

While the results are clear on the transfer of bacteria through double-dipping, the question of whether double-dipping actually spreads disease still remains. First, there are plenty of nasty illnesses you can get at a party that are viral in nature and not bacterial, like, for example, the flu. (That’s part of what makes it so challenging to get the most effective flu vaccine each season.) 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.

Second, we are covered in bacteria pretty much all of the time so unless you didn’t touch a door knob, shake anyone’s hand, or use your phone before you picked up that chip in the first place, it doesn’t matter if a double-dipper got there first. You’ve already transferred more bacteria to that chip than the dip ever could.

The Most Infamous Double-Dipper

The most infamous suspected double dipper may very well be Mary Mallon, more familiarly known as Typhoid Mary. She was an Irish American chef and also the first person in the U.S. known to be an asymptomatic carrier of typhoid fever. (In other words, she could pass on typhoid fever while displaying no symptoms herself.) She is suspected of having infected more than 50 people with typhoid fever in the late 1800s and early 1900s via her cooking. It has not been confirmed that she tasted her own dishes, but it is highly likely that she was able to spread typhoid fever in part due to double-dipping.

Mary was known for her lack of cooperation, including using aliases and refusing to admit to her possible role in the infections. She ultimately spent almost three decades of her life in forced isolation and we now use the term "Typhoid Mary" colloquially to describe anyone who unwittingly passes along diseases.

So while you may want to avoid that shared dip if you suspect double dipping has occurred, your best protection against the flu is getting your flu shot. And if you’re the one who is sick, or may have been exposed to a sick person recently, don’t be the “Typhoid Mary” of your holiday party and stick to single dipping that chip.

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.


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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