Let’s just admit it: We’ve all double dipped. Whether you’re at a frat party, a family dinner, or black-tie event, it just seems wrong to eat a chip without any dip. The logic when you take that half-eaten chip back for round two goes something like, How bad can it be, right?
As it turns out, double dipping can spread more harmful bacteria than you might have realized. In 2009, Clemson University food safety professor Paul Dawson wanted to find out just how bad this common cocktail party habit is so he gathered a team of researchers and conducted a study that was published in the Journal of Food Safety.
To understand how bacteria spreads at your standard buffet table, Dawson and his colleagues dipped crackers in three categories of “dip”: water, acidic water, and real-life dips (salsa, cheese dip, and chocolate dip). What they found was fairly surprising. According to the study, bacteria was most easily transferred through plain water—about 5,000 bacteria per milliliter to be specific. With acidic water, at a pH of 6.0, which better simulates the real food we eat, a cracker with a bite taken out of it transfers about 3,800 bacteria per milliliter. As for the actual dips we eat in daily living, the thinner the consistency, the more likely it is to spread bacteria from a slobber-coated chip.
To put it in simpler terms, bacteria is more likely to stick on the chip when you double dip in something thick like guacamole. With a thinner dip like salsa, the bacteria is more likely to spread throughout the rest of the bowl. You can find all of strains of bacteria transferred—Streptococcus, Prevotella, and Veillonella—in a healthy person’s mouth, but taken out of that context, they can sometimes cause infections.
“This is still significantly more bacteria than there should be,” Dawson says of their findings, and while “the odds are pretty low that it’s going to be dangerous, that is how common colds are spread.” Case in point, if you’re sick, just stay away from the communal foods altogether—for everyone’s sake.