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Can UV light negate the 5-second rule for food?

UV lights have gained popularity as sanitation devices after the rise of COVID-19. After all, UV light doesn’t involve harsh chemicals and is an easy way to wipe out almost all bacteria and viruses living on the surface of an object. It’s also easier than ever to obtain for yourself. Where UV light was once only used by medical facilities, handheld UV wands can now be purchased and used to clean countertops. UV light is also used to disinfect phones and tablets.

But what else can UV light be used on? If you go to a restaurant, can you use a UV wand to disinfect your food? Are there risks involved? With the heightened focus on sanitation and cleanliness, Digital Trends reached out to experts to find the answers to these questions. Is it possible that a UV wand could negate the 5-second rule?

The 5-second rule: Fact or fiction

Most everyone knows of the 5-second rule. If you drop a piece of food on the ground, as long as you snatch it up within 5 seconds, it’s safe to eat. Microorganisms won’t take hold that fast. If you really think about it, though, it doesn’t make sense. Ultimately, the 5-second rule is indeed myth — for the most part.

In 2017, Anthony Hilton, a professor at Aston University, spoke out in favor of the 5-second rule. He told Business Insider, “Obviously, food covered in visible dirt shouldn’t be eaten, but as long as it’s not obviously contaminated, the science shows that food is unlikely to have picked up harmful bacteria from a few seconds spent on an indoor floor.”

5 second rule
John Velasco / Digital Trends

There are multiple variables that come into play, including the moisture level of the food and the floor, the type of surface, and much more. Researchers from Rutgers University found that in some situations, bacterial transfer can happen instantaneously.

In short, the more moist a type of food — and the less frequently cleaned the floor — the more likely it is that dropped food is contaminated.

While you probably shouldn’t eat food that you dropped on the floor to begin with, what if it’s from a particularly good meal? Or what if it’s food from a restaurant, and you want to be extra-safe concerning COVID-19? Can UV light help then?

Possibly, but not in the way you think.

An industrial UV lamp
sergeyryzhov/Getty Images

UV light takes time to clean

There are three main types of UV light: UVA, UVB, and UVC. UVA and UVB are the most common types of UV produced by the sun, with longer wavelengths than UVC. While all types of UV light can cause skin damage and skin cancer, according to the American Cancer Society, UVB rays are thought to cause most skin cancers. UVC rays are the most energetic type of UV light and usually do not reach the ground.

UVC is the type of UV light used to clean and disinfect surfaces. It has a wavelength between 200 and 280 nanometers, but its ability to destroy bacteria and viruses is also what gives it the ability to cause skin cancer.

Many people use the UVC wand as a sort of “flash” cleaning, but UVC light requires prolonged exposure to be truly effective. A 2014 study in the American Journal of Infection Control found that portable UVC wands killed most commonly-found bacteria after 5 seconds of exposure, and were able to eliminate 90% of harder to kill bacteria after 40 seconds.

UVC light is also only effective at surface-level cleaning. Without getting too scientific, the shorter wavelength makes it less effective at penetrating surfaces. UVC light is most effective when cleaning flat surfaces, as well.

UV light is used in the food industry for disinfecting purposes, but not for food itself. UV light sees most of its use in sanitizing surfaces in processing facilities. In a paper from the National Center for Food Safety and Technology, Tatiana Koutchma says “applications include decontamination of surfaces of equipment in bakeries, cheese and meat plants…and for decontamination of conveyor surfaces and packaging containers.”

5 second rule with UVC light wand
John Velasco / Digital Trends

Again, this application uses significantly more powerful UV light than what is emitted by consumer-grade wands. It is also applied to flat surfaces. There are applications that include using UV light on actual consumables, as laid out in a paper published in Ozone Science and Engineering, also by Tatiana Koutchma: “Its applications include pasteurization of juices, post lethality treatment for meat, treatment of food contact surfaces and to extend the shelf-life of fresh produce.”

The level of UV light used in industrial food applications is far stronger than that available to consumers. Due to the increased intensity and more thorough application, its disinfecting and sanitary properties are more pronounced than what is available in a consumer-grade UV wands.

Can UVC light clean your food after you drop it? Yes, perhaps — but it may take more time than it is worth to ensure a thorough clean. The uneven shape of food would require you to use the UVC wand at different angles to ensure all of its surface was clean.

A UVC wand would also only clean the surface, so any bacteria inside the food itself would remain and would still make you sick upon eating it.

The risks of UVC light

Like any cleaning tool, UVC wands should be handled with care. While proper use is not likely to cause too much skin damage, UVC light can still be harmful in large doses, particularly if you are using the wand on a regular basis.

According to Stephen Holler, Professor of Physics at Fordham University, “Whereas UV-A can penetrate the skin deeply, UV-C is unable to get beyond the surface layer of dead skin cells. This helps keep it from doing much damage to people. However, bacteria and viruses are sufficiently small that it is able to penetrate their structures and do significant damage, effectively “killing” them and rendering them harmless.”

Most UV wands are intended to be used close to the object you are cleaning and turned away from you. Looking into the light can cause damage to your eyes, and using the wands on your skin is inadvisable. Although much of the light may be blocked, you can still harm the skin cells on the surface of your skin.

Does the 5-second rule matter?

If used correctly, it seems like the UVC wands could actually negate the 5-second rule. The ironic aspect is that you will need more than 5 seconds to properly clean all the surfaces of your food. The more advisable course of action is to leave any dropped food in the trash and just go for another, worry-free bite.

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