How Gross Is the Five-Second Rule? Is Double-Dipping Dangerous? This Book Reveals the Truth
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Creativ Studio Heinemann

This Book Reveals the Truth About All of Our Grossest Food Habits

From double-dipping to beer pong hygiene, Paul Dawson and Brian Sheldon are exploring the nastiest questions of food science.
October 16, 2018, 6:00pm

There’s a well-known Seinfeld episode called “The Implant” that viewers of the show might remember for its titular plotline, which revolves around Jerry’s suspicion that his girlfriend, a pre- Desperate Housewives Teri Hatcher, has fake breasts (memorable line: "And, by the way, they're real… and they’re spectacular!"). But as a George Costanza superfan, my more impactful memories are of the episode’s subplot, in which Larry David’s socially inept alter-ego travels to Detroit to attend his girlfriend’s aunt’s wake. George then gets into quite the kerfuffle at the snack table, when the girlfriend’s brother attacks him for “double-dipping” a chip: “That’s like putting your whole mouth right in the dip!” he cries.

As the polar opposite of a germaphobe (a subject the show memorably dealt with a second time in “The Apology,” when Kramer serves an entire meal he prepared while bathing), I’ve never been bothered by sharing drinks or ice cream cones, and double-dipping doesn’t make me bat an eye. But after speaking with food scientist Paul Dawson, co-author, along with Brian Sheldon, of the new book Did You Just Eat That? Two Scientists Explore Double-Dipping, the Five-Second Rule, and other Food Myths in the Lab, I’m changing my tune.

In the book, Dawson and Sheldon—based, respectively, at Clemson University and North Carolina State University—take those myths into the lab, where they test eaters’ assumptions that food that just fell on the floor is still good and that beer pong is sanitary enough (the alcohol in the beer disinfects the ball, doesn’t it?). Perhaps unsurprisingly, the authors find that these common eating habits—ones that Costanza would no doubt embrace—aren’t so inconsequential, with the potential to transfer significant amounts of bacteria and even the possibility of illness to those who indulge.


Dawson told MUNCHIES that the idea for the book came about long ago, back in 2007 when the food scientist and then- New York Times columnist Harold McGee wrote a piece about Dawson’s meticulous lab study of the “five-second rule.” That study, conducted that year at Clemson, found that pieces of bread and bologna subjected to five seconds’ exposure to salmonella-painted surfaces picked up measurable quantities of the bacteria, with numbers climbing even higher when the food was left for a full minute. The article generated so much interest that Dawson and Sheldon decided to expand their testing of other little-examined eating habits.

We spoke with Dawson about why sharing a bag of popcorn and even just touching restaurant menus are much, much ickier than you ever thought.

MUNCHIES: Hi, Paul. So I thought we’d start with double-dipping. What’s the problem with it?

Paul Dawson: The main thing we found that there is bacterial transfer during double-dipping. There's no way of knowing how many people have gotten sick from it, but I'd be willing to bet there’s at least one. If you're at a party and someone's sick, and then later on you're sick, you might wonder what happened.

"The students actually call this [Beer] Pong Flu. If they play some tournaments, they'll start getting sick."

And what about the five-second rule? Is there any length of time that's acceptable, or is the transfer of germs instantaneous?

It's instantaneous. Bacteria don't have to jump; they make contact on the surface. There are numerous studies on this, and some of them have come up with reports that say, “Well, it's okay if you do it 30 seconds.” We found that there's significant differences in bacteria accumulation over time, but even though there's differences between five seconds and 60 seconds, there's still immediate transfer.


So then the question is, is it really a problem? And my point would be, well, not really, because most surfaces aren't going to have pathogenic bacteria on them. But on the other hand, if it is there, it is going to be transferred. It's kind of like wearing a seatbelt or not. You can not wear a seatbelt your whole life and never have an accident and you never get hurt. But if you do have an accident, the odds are better you're not going to get hurt. It’s the same thing with not eating food dropped on the floor.

"One of them was blowing birthday candles out. We found pretty high levels of bacteria in some cases. Actually, I found while researching other studies that these bacteria are flying out of people’s mouths even just in conversation."

How about with beer pong? What are some of the results you came up on that one?

To test it, we went out to kids playing the real game, since it was homecoming weekend at Clemson. And we found very high levels of bacteria on some of the ping pong balls. The problem with taking random samples is that it's random. But the point is that we look at both the maximum and the minimum. We found up to 3 million bacteria on one ping pong ball. That was a game that had been played outdoors.

When you play beer pong and you lose, you gotta drink beer. And then you gotta go to the lavatory, where you might not wash your hands, and then you drink. So it's a vicious cycle of transfer of bacteria from the ball to the beer, to someone's hand, and back to the beer again.


The students actually call this Pong Flu. If they play some tournaments, they'll start getting sick. They're not sure whether it's from drinking too much, or if it's actually from drinking beer that's got bacteria in it.

beer pong

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When you were examining these different practices, were there any results that surprised you, like a practice you thought was benign but it turned out not to be?

One of them was blowing birthday candles out. We found pretty high levels of bacteria in some cases. Actually, I found while researching other studies that these bacteria are flying out of people’s mouths even just in conversation. There are some studies where people who have tuberculosis or the flu come in the room, and from coughing or even just breathing, the number of virulent particles that are in the air are pretty high.

So is all of this actually bad for us? Doesn’t ingesting bacteria help keep our immune systems strong?

There's definitely something to the “hygiene hypothesis.” In the US and other modernized countries, we’ve seen a decrease in infectious diseases, but an increase in autoimmune and allergic diseases. There's a theory that being so clean, so not exposed to bacteria, that the body doesn't learn the difference between harmful substances and the ones that aren't. So then the body triggers more of these autoimmune diseases.

Clearly, it's good to be exposed to bacteria at a young age. On some level, that helps to develop an immune system. But I just always kind of circle back to say: “Yes, but…” We know that bacteria can actually increase things like asthma, or a respiratory virus, and might cause other health problems. I think there's some truth on both sides of the argument, but from a safety standpoint, there are still things that can overwhelm your immune system. I don't know if the risk is worth it.

Thanks, Paul.