In Too Afraid to Ask, we’re answering food-related questions that may or may not give you goosebumps. Today: Does double-dipping spread germs?
It was a 1993 episode of Seinfeld that inspired Paul Dawson, PhD, to study double-dipping. In “The Implant,” George double-dips a chip at a wake and is razzed by Timmy, who tells him that it’s like “putting your whole mouth right in the dip.” Dawson, a food scientist at South Carolina’s Clemson University, wanted a real-world research example so that he could to teach his students how to conduct studies, and Timmy’s line gave him “a hypothesis to test,” he tells me.
Dunking a carrot into a bowl of hummus, taking a bite, then dunking again, seems harmless enough when you’re by yourself. It’s your carrot; it’s your hummus. (Who hasn’t double-dipped from the comfort of their own couch?) But in social settings, double dipping has long-been the subject of debate.
Nobody cares what you do at home, says Nick Leighton, an etiquette expert and host of the Were You Raised by Wolves podcast. “If you’re eating guacamole alone, then have at it,” he says. “But once other people are involved, the rules of etiquette apply.” The way we behave in public sends signals to those around us, says Leighton, and double-dipping makes people nervous. “I don’t want your mouth on the food I’m about to eat,” he says. To him, double-dipping creates trust issues. “The mind wanders,” he says. “What else are you capable of doing?”
Scientifically, though, was Timmy right in scolding George for double-dipping at the wake? “Absolutely,” says Dawson, who conducted various experiments with his students to study the germ trail left behind by double-dippers, like measuring the bacteria left behind after dipping bitten crackers in various dips. “There were between 100- and 1,000-times the number of bacteria transferred to the dip when a chip was bitten before dipping compared with when the chip was dipped without biting first.”
Here’s what you need to know about double-dipping—and how you can politely prevent Uncle Bill from contaminating the queso.
What are the health risks associated with double-dipping?
The primary concern with double-dipping revolves around the potential transfer of oral bacteria and saliva from an individual’s mouth back into the communal dip, via some sort of dunking vessel.
“The mouth is home to a number of bacteria” that are perfectly normal, says Harjot Singh, MD, an infectious disease specialist at Weill Cornell Medicine. That said, not everything lurking between your molars is quite as benign. Streptococcus, depending on the species, is common and can cause cavities. There are also oral bacteria and viruses in the mouth that could spread via saliva, Dawson says, citing meningitis, pneumonia, influenza, and more. COVID falls into this category too.
In his 2009 research on the microbial consequences of double-dipping, which remains the most widely referenced study on the practice, Dawson found that the practice does transfer bacteria from mouth to dip. Initially, students assessed the bacterial transfer from a cracker to a cup of plain water. They found that the chomped cracker dipped into the water yielded approximately 1,000 more bacteria per milliliter than an unbitten cracker.
