The Five-Second Rule?

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.five_second

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.icecream

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 Sources:

5 thoughts on “The Five-Second Rule?

  1. Mairead Donnard

    This was such an interesting blog! When I was younger, I definitely lived by the five second rule. Although as I have grown older, I realize how unsanitary that can be. It can be concluded that both studies found that regardless of time, bacteria was transferred. This is definitely concerning being that a lot of people blindly follow this rule. I think that regardless of the facts that back this rule, many people will still continue to eat food off of the ground regardless of time. With this being sad, here is an interesting video about the five second rule: . It introduces the fact that bacteria moves at the speed of .00045 mph aka extremely fast. Based on your blog and this article, it is wise for people to not live by the five second rule.

  2. Rebecca Aronow

    This post was really interesting to read, especially because I’m always unsure as to whether I should pick up dropped food off the ground and eat it. If I drop, for example, a piece of penne pasta, I will throw that out because my logic has determined that the wetness of the pasta will hold onto more germs. But if I were to drop a pretzel, I would probably pick that up and eat it because I think it’s dry and the bacteria hasn’t gotten to it/stuck to it yet. It was interesting to read about the amount of germs that transfer to foods depending on the type of food, type of surface, and amount of time that the food is left on the ground. But I also think it’s interesting to examine why some people are okay with eating food off of the ground even if they have the knowledge that there is probably some bacteria on it. I found this New York Times article that mentioned the study that you cited in your blog and it also talked about why we have developed this concept of the “five-second rule.” Psychologist William K. Hallman refers to heuristics, rules that we form through our own experiences and what we’re told that allow us to make decisions quickly. These heuristics, however, often don’t take in all of the facts. The fact that bacteria is invisible allows us to view it as less threatening. This made me think about my pasta example. A piece of dirt is more likely to visibly stick to a piece of pasta than a pretzel. This piece of dirt, in my mind, represents bacteria and therefore makes me realize the germs that are on that pasta. This knowledge causes me to throw that food out versus eat it, like I would with the pretzel because I can’t see that piece of dirt. Douglas Powell also states that we abide by this five-second rule because we have been trained that wasting food is bad. So, overall, our general lack of knowledge about germs, how they work, and how they affect us allows us to believe that this five-second rule is correct, when in reality, if we analyze the scientific research as well as the psychological explanations behind this “rule” we probably would stop eating food off the floor, even if we pick it up right away.

  3. Xueyao Cao

    Interesting topic to discuss about. Personally I don’t pick up food from the ground just to be safe. Before reading your blog, I went on youtube and found some videos which conclude the opposite idea, that five second rule is true.
    It seems really convincing to me until I read your whole blog post and think about. It is true that our brain is lousy and sometimes we couldn’t think about the issue in different angles. The video there conclude that it is true, because it says the transfer speed of the germs are slow. As I read your blog and the comments from other people, I found there are more third variables than I thought there would be at first, such as the material of the ground and the type of food. Another thing I come up with is that, this might do with priming as well. Do people really believe in this rule or not? I think that sometimes our sub consciousness and priming would cause us to get ill or not.
    Also, I found out another video that analyse the rules and produced several more studies.

  4. Pedro de Mello

    I like this because the Mythbusters actually did an experiment on the validity of the 5 second rule once. Basically, what they found is that the time the food is exposed to the floor is less important than the surface area exposed. Since bacteria don’t actually move towards the food when it’s dropped, all that matters is how many of them dropped food is exposed to when dropped. I found it very interesting, and while I haven’t really ever believed on the rule, Adam and Jamie totally killed all doubt I could have had.

  5. dhc5097

    I found this post extremely interesting because I have many friends that abide by this “5 second rule.” I’ve always wondered if it actually took bacteria 5 seconds for it to adapt and stick to the food that had been dropped. Know that I know that the 5 second rule is not actually accurate I wonder what that means for other objects that fall on the ground for a short amount of time until we pick them up, such as a pillow, towel, hat, etc. All these items come close to our face, body and hair but we seem to ignore the issue of all the germs touching them when they fall on the floor for a couple of seconds. I found an article online that discusses the worst place you can possibly pick up germs regarding items we come in contact with about everyday.

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