It turns out that many of the things we do to keep ourselves safe from harmful bacteria just make the problem worse
Here’s a germaphobe alert: There are likely more bacterial cells in and on you right now (39 trillion, on average) than there are actual human cells (around 30 trillion). Most of them are harmless, or even good for you, but some are pernicious. One in six Americans, for instance, comes down with an illness from food-borne microorganisms each year, according to the Centers for Disease Control.
So how do we avoid the harmful bacteria? There are some basic rules to observe: Wash your hands frequently when touching surfaces and before handling or eating food. Cook food to proper temperatures, and store leftovers properly.
But as specialists in food science and food microbiology, respectively, we’ve also spent some years exploding myths about what is and isn’t safe and highlighting some unexpected risks. A few examples:
The five-second rule: Many people believe that a piece of food dropped on the floor is safe to eat if you pick it up quickly enough. The idea is that bacteria don’t have time to transfer in under five seconds. But that’s plenty of time for nasty bacteria to “leap” onto a piece of food.
We tested the five-second rule in our laboratory at Clemson University by dropping bologna and bread on surfaces contaminated with Salmonella. We recovered between 100,000 and 10,000,000 bacteria after five seconds, depending on the surface, as we reported in 2006 in the Journal of Applied Biology. Admittedly, waiting 60 seconds is worse—about 10 times worse, in our research—but five seconds is bad enough.
Ice cubes and lemon juice: Many of us think that the ice in our drinks is safe and that the acid from a lemon slice dropped in a beverage reduces any contaminating microorganisms. But both can carry potentially harmful pathogens themselves. A 2007 study by two clinical microbiologists published in the Journal of Environmental Health found that 70% of lemon slices from the rims of glasses in restaurants produced microbial growth; 25 different microbial species were found on the samples.
‘ Even when you blow out birthday candles at your party, you spread bacteria. We tested it. ’
In our own study published last year in the Journal of Food Research, we found that 60% and 80% of the E. coli bacteria that we introduced onto hands and scoops, respectively, were transferred to a drink via ice cubes. For lemons, an average of 6,000 E. coli were transferred to wet lemons touched by our participants’ hands, and then they multiplied—a sixfold increase over 24 hours at room temperature.
Restaurant hazards: Food and drink aren’t the only risks to your health when you’re eating out. A study published in the Journal of Environmental Health in 2013 by U.S. and South Korean researchers found that Salmonella and E. coli can survive for up to 72 hours on laminated plastic menus (on paper menus the strains lasted only six hours).
We checked this ourselves by inoculating plastic menus with a fluorescent E. coli strain and then asking participants to handle the menus for one minute, as if they were ordering food. About 11% of the bacterial cells, or an average of 3 million, were transferred to hands. Knowing this, you might want to keep a bottle of hand sanitizer ready for the next time you dine out—but then again, see the next point.
Hand sanitizers: How many of us carry around a small bottle of hand sanitizer, just in case? Unfortunately, they are not as effective as a thorough hand-washing regimen. A sanitizer advertising that it removes “99%” of the microbe population can still leave thousands of viable organisms per square inch, depending on the initial population.
And that’s only for the specific types of organisms the products are designed to kill, not for all of the ones you encounter in real life. To get U.S. Food & Drug Administration approval for the antimicrobial agents used in hand sanitizers, manufacturers test them against only a select number of bacteria, not including E. coli and Salmonella.
Hand dryers: If you use soap and water instead, you may then dry your hands with a hot-air hand dryer in the restaurant restroom. Those dryers are actually blowing bacteria around. Bioaerosols are generated in restrooms with every flush of the toilet, and then hand dryers circulate the water droplets around the room.
A 1993 study at the University of Westminster in the U.K. found that electric hand dryers increase bacteria on hands after washing by fivefold, while paper towels decrease bacteria by 42%. Subsequent studies have had a wide range of results but have confirmed that air dryers spread bacteria.
Another Westminster study in 2015 found that today’s jet-air dryers spread bacteria twice as far—6 feet, on average—as older air dryers. In our own tests in 2016 around the city of Clemson and our campus, we found that gas-station hand dryers were a little cleaner than college dormitory hand dryers, but those in grocery-store bathrooms circulated nine times more bacteria than the other two.
You can’t even try to avoid most of the bacteria that’s floating around us all the time. Even when you blow out birthday candles at your party, you spread up to 37,000 more bacteria onto the cake than it had before the guests sang “Happy Birthday.” (We know because we tested that, too.) Which leads to our final piece of advice: Try not to think too much about those trillions of bacteria swirling around you.