True or False? Lots of mums know the five-second rule, a common superstition which says that food dropped on the ground will not be contaminated with bacteria if it is picked up within five seconds of being dropped.

Jorge Parada, MD, MPH, FACP, FIDSA, medical director of the infection prevention and control program at Loyola University Health System has attempted to provide the answer: “A dropped item is immediately contaminated and can’t really be sanitized. When it comes to folklore, the ‘five-second rule’ should be replaced with ‘when in doubt, throw it out’.”

Parada says that everything that comes into contact with a surface picks up bacteria and dirt, but how much bacteria and what kind of microbes contaminate an object depends on what item has been dropped and the surface it has been dropped on.

Parada, who admits to also occasionally using the five-second rule himself, says:

“If you rinse off a dropped hot dog you will probably greatly reduce the amount of contamination, but there will still be some amount of unwanted and potentially nonbeneficial bacteria on that hot dog. Maybe the dropped item only picks up 1,000 bacteria, but typically the innoculum, or amount of bacteria that is needed for most people to actually get infected, is 10,000 bacteria – well, then the odds are that no harm will occur. But what if you have a more sensitive system, or you pick up a bacteria with a lower infectious dose? Then, you are rolling the dice with your health or that of your loved one.”

Another habit often used by mums is to “clean off” a baby’s pacifier that has been dropped using their own mouth. Parada, who is a professor at Loyola’s Stritch School of Medicine, explains: “That is double-dipping – you are exposing yourself to bacteria and you are adding your own bacteria to that which contaminated the dropped item. No one is spared anything with this move.”

Parada likes to compare the issue of being exposed to bacteria with that of being burned, saying that the temperature and time are comparable to the type and amount of bacteria. He explains:

“The hotter the surface the easier and worse you will be burned – like the more virulent, or harmful, the bacteria the easier and sicker you may get. One only has to touch a white hot surface momentarily to get burned and sometimes it doesn’t take a lot of bad bugs for you to get sick. On the other hand, if hold your hand to a less hot surface, but do so for a longer period, the more you will be injured, too.”

He continues to explain that there are varying degrees regarding the contamination risk, saying: “So, a potato chip dropped for a second on a rather clean table will both have little time to be contaminated and is likely to only pick a miniscule amount of microbes – definitely a low risk.”

However, food that lands and stays for a minute on a spot that is possibly more contaminated, like a floor, will collect more bacteria and pose a greater risk.

Parada continues explaining: “In the same time period, a rock candy is less likely to pick up contamination than a slice of cheese. As an extreme example, whether it’s a rock candy or a slice of cheese, I don’t think anyone would invoke the five-second rule if it fell in the toilet. At the end of the day, this is a polite social fiction we employee to allow us to eat lightly contaminated foods.”

When asked whether the old saying that exposure helps to build a healthy immune system is correct, Parada explained:

“There actually is certain research that supports the importance of being exposed to bacteria at critical times in a child’s development. But I believe this development applies to exposures of everyday living. I do not advocate deliberately exposing ourselves to known contaminants. That would probably be a misplaced approach to building up our defenses. If you want to be proactive in building up your defenses, eat right, exercise, and adequate sleep – and remember to get your vaccines.”

In a later study, published in Medical News Today in March 2014, researchers have suggested that the 5-second rule is not an urban myth.

Written by Petra Rattue