I’ll admit it; I’m a huge germaphobe. Thinking about germs and sickness freaks me out, and I would never dare to go without washing my hands after using the bathroom. As a result of my aversion to germs, I abide by some personal rules, one of them being that if a piece of food falls to the floor, I don’t eat it. However, popular wisdom has a different approach to this scenario: if a piece of food falls to the floor, a person has exactly five seconds to pick up a piece of food and eat it after it’s made contact with the ground. This is known as the five-second rule, and it supposedly works because the theory is that the bacteria won’t reach the food before that time limit. Naturally, as a self-proclaimed germaphobe, I find this rule to be disgusting and have never followed it myself. But I am interested to know if I am correct in my dismissal of this logic, or if the five-second rule actually works.
On the surface, there is a lot to consider in the five-second rule—time, bacteria, food, and sickness. It can be an overwhelming proposition, leaving people to just assume it’s correct. But the problem can be boiled down into a testable hypothesis: if food dropped on the floor is picked up in five seconds or less, then it will have less bacteria on it. While we are definitely concerned about the sickness that the germs can cause, this is a hard endpoint, and it is pretty difficult to determine whether a sickness would be caused specifically by the food that was dropped on the floor. Testing just for whether or not someone got sick would make for an experiment riddled with confounding variables. It also eliminates the possibility of reverse causation, since it doesn’t make any sense the other way around; food having less bacteria wouldn’t cause someone to pick up food within that time frame. How would the average person know how much bacteria are on a piece of food? If I were to personally perform an experiment, this would be the setup for my hypothesis.
However, I’m not a scientist, so let’s see what kinds of tests have actually been done to test out the so-called “five-second rule.” Does it hold up in practice? In fact, many scientists have actually found it doesn’t, and other factors come into play besides the timing. Time, type of food, and surface material all have an impact as well, according to a study published by researchers at Rutgers. They tested four different types of food, four different surfaces, and four different times for the food to come in contact with the bacteria. To start, the scientists infected an area on each type of surface with a type of bacteria known to cause infections, and then tested each piece of food for each length of time. The researchers concluded that while more bacteria was transferred the longer the food remained on the surface, some of that bacterial transfer happened right away. If bacteria can be found on food right after it’s dropped, this would mean that the five-second rule doesn’t work. The type of surface also made a difference; the transfer rate of bacteria was generally lower when it was on carpet as opposed to tile.
While this was a helpful study to use to see if the five-second rule works or not, it’s also a study that has a lot going on in it. It shows that the amount of time a food makes contact with the floor does play a role, but it’s just one of many confounding variables. The lack of one clear causal variable and one response variable makes it difficult to determine the link between time and bacteria count.
To try to narrow down the issue, I looked at another study. Again, this study tested all three variables: food type, surface type, and contact time. However, the first two variables were reduced in that only two types of food and three types of surfaces were tested. In this experiment, the researchers infected the surfaces with a form of salmonella, and then tested the two types of food over different amounts of time. Once again, it was found that bacterial transfer was significantly greater coming from tile versus carpet. Wood was also found to have a higher transfer rate. The study also drew the same conclusion about contact time and found that bacteria can be transferred to foods right as it hits the ground.
The multiple factors that went into each study make it difficult to answer my initial question, and I think the issue is even more complex than I originally thought. I didn’t even think to consider the type of surface or food in my initial thoughts. These are all confounding variables we have to think about. However, both studies did conclude that bacteria could be transferred to food in less than five seconds, therefore making it likely that the five-second rule is not a good one. So, in the end, I’m going to stick to my germ-fearing ways and steer clear of any food dropped on the floor.Image Sources: