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Home » Public toilets fill air with aerosols of feces and urine — mask up

Public toilets fill air with aerosols of feces and urine — mask up

Last updated on February 7th, 2023 at 02:54 pm

I’ve got something new for you — a newly published study warns that public toilets create aerosols of feces and urine that can be detrimental to your health. If you want to protect your health, here is one more reason to wear a face mask.

I’ve always wondered about public toilets with energetic flushing mechanisms that flush the toilet more vigorously since they get more use than your home toilet. It’s cheaper to have these strong flushing mechanisms in public restrooms than to hire people to clean them more frequently.

But that flushing mechanism is so robust that it causes aerosols that contain bits of poo and pee that you inhale. I don’t really want to think about this, but we are breathing all this sewage while we’re in a public restroom.

As I always do, let’s take a look at this new peer-reviewed paper that examines what we’re inhaling while in public restrooms. It’s not going to be pleasant.

toilet signage beside green leaf
Photo by Hafidz Alifuddin on

The pee and poo aerosols in public toilets paper

In a paper published on 8 December 2022 in Nature’s Scientific Reports, John P Crimaldi, Department of Civil, Environmental, and Architectural Engineering, University of Colorado, and colleagues used laser light to illuminate ejected aerosols to quantify the kinematics of plumes emanating from a commercial flushometer-type toilet and use the motion of aerosol particles to compute velocity fields of the associated flow.

That really does sound like a lot of engineering, but remember, the “ejected aerosols” contain feces and urine, not pure spring water. And what they found was that the toilet flush produced a strong chaotic jet with velocities exceeding 2 meters per second. I was surprised by this number.

Measuring aerosols from a public toilet

Furthermore, the researchers found that this jet transports aerosols to heights reaching 1.5 m within 8 seconds of initiating a flush. In other words, those aerosols filled with urine and fecal material will reach the height of your mouth and nose within eight seconds. And I should note, that you might get away from your own flush during those eight seconds, but any other toilets flushing, usually from complete strangers, are also flooding the restroom with those aerosols.

This is a convincing study that shows that large amounts of aerosols are formed when you or anyone flushes a toilet in a public restroom. Remember, those aerosols contain a lot of fecal and urine material that gets right into your lungs.

Now this paper didn’t measure actual fecal solids or show that actual pathogens were transmitted. It just shows that commercial toilets produce significant aerosols, and it’s easy to conclude that those aerosols will contain particles of feces and urine.

Why is that a concern? The feces and urine can contain numerous pathogens such as SARS-CoV-2, the virus that causes COVID-19. Research has shown that the virus can persist in stool for months after the infection clears in the respiratory. I can’t begin to list out the potential pathogens that exist in feces — polio, enteroviruses, coliform bacteria, pathogens that cause gastroenteritis, and much much more. And let’s not forget COVID-19.

With polio showing up a bit more frequently, it is best to remember that polio is transmitted by the fecal-oral route. So you don’t know if the person in the next stall has some disease that comes out in their poo — then they flush, and you get several deep breaths of their aerosolized fecal material. Yuck.

I’m a devoted mask wearer — I am wearing a KN-95 mask right now as I am writing this article in a public area. And when I use a public restroom, my mask is always on, because I’ve known for years that toilets aerosolize feces and urine. In fact, I have always kept my toothbrushes in the kitchen, not the bathroom, just because I do not want my fecal material getting on my toothbrush.

I’m not trying to give you something else to fear in the world, but this has always been a concern of public health people. And now we have data on how these public toilets produce aerosols that can contain feces infested with pathogens.

Wear your mask when you head to a public restroom. It might protect your health.


Michael Simpson

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