What actually happens in those few seconds between pressing the lever and turning away? On 5ch’s Science News+ board, users discussed a study out of Flinders University in Australia that pulled together 22 past studies on the aerosols produced when a toilet is flushed. According to the review, the violent motion of the flushing water can send tiny particles laden with microorganisms flying all the way up to the height at which an adult breathes, with some particles reported to stay airborne for more than 20 seconds. It’s a fairly fresh piece of research — published online in August 2026 and covered as news by the university on September 7. The thread saw a wave of “closing the lid before flushing is just common sense” comments, alongside cooler reactions like “never had a problem” and “quit putting out announcements just to stoke anxiety,” showing just how differently people weigh the risk.
Flushing the toilet found to send bacteria flying up to “breathing height”
You finish your business, press the lever, and turn away. It all happens in those few seconds.
Bacteria and viruses tend to linger in the toilet bowl — that’s exactly why we wash our hands.
Researchers at Flinders University compiled and analyzed 22 past studies on the aerosols/bioaerosols released when a toilet is flushed. In other words, the researchers themselves didn't run brand-new experiments on 22 different toilets — this is a review of existing data.
The key points that came out of it are roughly these:
The violent movement of the flushing water releases fine droplets and particles into the air
Depending on how contaminated the bowl is, these can include bioaerosols carrying bacteria and other microorganisms
Some past studies confirmed these particles reaching the height at which an adult breathes
In at least some studies, particles stayed airborne for more than 20 seconds
In experiments where microorganisms were deliberately added to the bowl water, higher microbial concentrations in the water led to more microorganisms detected in the air
In general, larger flush volumes tended to produce more aerosols
3AnonymousSep 14, 2026 23:00
Existing research suggests that closing the lid can cut down on larger particles being scattered upward, but fine aerosols may still escape through gaps around the seat and lid. This review also didn't find sufficiently consistent evidence either way on how much the lid affects aerosol concentration.
So the most accurate way to sum up where things currently stand is something like:
"Flushing a toilet can release more airborne microorganisms than people assume — but exactly how much that translates into real-world infection risk is still unclear."
For reference, this study was published online on August 1, 2026, and Flinders University covered it as news on September 7. So the article in question is reporting on quite recent research.
4AnonymousSep 14, 2026 23:08
Back in my student days, I once tested the water sitting in a flush toilet for E. coli counts, and I remember being surprised it came out to only a dozen or so per cc — way less than expected. Though I took the sample in the morning, so the number might have been right after cleaning. Point is, if you clean the toilet daily you probably don't need to worry.
5AnonymousSep 14, 2026 23:19
Huh? Only now? Again? Seriously, this old thing?
6AnonymousSep 14, 2026 23:27
So is a squat toilet or a pit latrine the safer choice, then?
7AnonymousSep 14, 2026 23:34
So what? Nothing's ever happened to us. Quit putting out announcements just to stoke anxiety.
8AnonymousSep 14, 2026 23:42
I mean, poop comes out of the human body in the first place (so of course it's full of bacteria).
9AnonymousSep 14, 2026 23:46
That's why you put the lid down before you flush.
10AnonymousSep 14, 2026 23:57
But I've never once gotten sick from it.
11AnonymousSep 15, 2026 00:08
Personally I figure the farts you let out before and after dropping a deuce with your pants down already send trace amounts of gut bacteria into the air.
12AnonymousSep 15, 2026 02:24
This is a business opportunity — bet TOTO and LIXIL will come up with something for it.
13AnonymousSep 15, 2026 02:32
This got beaten to death during the pandemic.
15AnonymousSep 15, 2026 03:10
Eh, if anything it'll toughen up your immune system.
16AnonymousSep 15, 2026 03:51
Isn't it as simple as just closing the lid before you flush?
17AnonymousSep 15, 2026 04:03
Re: #1 People have been saying that forever. With a Western-style flush toilet, closing the lid before flushing is common sense — this isn't some 10-year-old idea, it goes back way further.
18AnonymousSep 15, 2026 04:05
Public toilets are crawling with other people's poop bacteria. Your own home is crawling with your family's poop bacteria. Even at the public bathhouse, other people's poop bacteria are floating in the water.
19AnonymousSep 15, 2026 04:05
Huh? Only now? This got hammered on endlessly during COVID — "close the lid before you flush," remember? Japanese universities were already running scientific studies proving it around when COVID started spreading, too. Though whoever did it first was probably somewhere else, even earlier than that.
21AnonymousSep 15, 2026 05:07
So what? Do you have any idea how many germs are already floating around your room?
22AnonymousSep 15, 2026 05:46
Just take down the "science news" sign already.
23AnonymousSep 15, 2026 05:52
That's a different beast entirely, unlike your average Zaku. (a famous line from Gundam's Char Aznable, used here as a stock meme to say "this one's on another level")
24AnonymousSep 15, 2026 07:05
Is this a Febreze commercial?
25AnonymousSep 15, 2026 09:39
Doesn't seem like it needs to gush out that hard… if it worked like those old countryside pit toilets, where a flap swings out of the way and then just a trickle flushes through, things would go a lot smoother.
30AnonymousSep 15, 2026 11:55
Re: #25 It has to flush everything all the way through the pipes to the sewer (or septic tank), so of course it needs that much water. A pit toilet can get away with less because the tank sits right underneath.
26AnonymousSep 15, 2026 10:08
Did you actually close the lid?
27AnonymousSep 15, 2026 11:18
I'm doing just fine, and it's my own waste anyway — life gets exhausting if you sweat details like this.
28AnonymousSep 15, 2026 11:44
I've lived 72 years like this with zero problems, so it's not an issue. Worry about stuff like that and you'll go bald.
29AnonymousSep 15, 2026 11:53
I always close the lid before flushing. Leaving it open is unthinkable to me.
31AnonymousSep 15, 2026 12:06
When you smell poop, that means poop-smell molecules are literally sticking to the mucous membrane in your nose.
34AnonymousSep 15, 2026 12:32
Re: #31 Yeah, like skatole and such — totally harmless.
32AnonymousSep 15, 2026 12:20
I'm pretty sure there's a high-rise apartment tower somewhere in the Middle East that still uses pit toilets…
33AnonymousSep 15, 2026 12:30
In terms of bacteria, toilets are actually pretty clean — the kitchen is the real danger zone.
35AnonymousSep 15, 2026 12:37
It really all comes down to quantity, but the human brain just isn't built for judging risk in degrees — it wants a binary safe-or-unsafe answer.
36AnonymousSep 15, 2026 12:40
Everybody already knew this.
37AnonymousSep 15, 2026 12:50
You should worry less about the sheer number of germs and more about which species they are and how infectious they are.
39AnonymousSep 15, 2026 12:55
C'est la vie. Humanity's done fine with this forever, so don't sweat it. Just put the lid down before you flush.
40AnonymousSep 15, 2026 12:55
Re: #1 You see this trick a lot — visualizing something invisible to make it look extra dirty — but we've been fine regardless, right? Isn't it just normal for both the human body and the environment to be full of germs, microbes, and aerosols?
41AnonymousSep 15, 2026 13:03
I heard about this ages ago and have made a habit of closing the lid before flushing ever since. Isn't that basically common sense for Japanese people by now? So now they're moving on to making a fuss about the possibility of it escaping through gaps around the seat and lid?
Background and key points of this discussion
Worth noting: this study didn’t run fresh experiments on any particular toilet — it’s a review paper that compiled and evaluated data from 22 previously published studies. Rather than fresh measurements for specific toilet models or flush volumes, it’s an organization of existing findings, published online in August 2026 and spreading as a relatively fresh topic once Flinders University covered it as news on September 7. Where opinion in the thread split was over just how effective the lid-closing habit really is. While many called it “common sense,” the review itself says it found no sufficiently consistent evidence on how the presence of a lid affects aerosol concentration, so closing the lid can’t be called a guaranteed fix. It’s also worth separating the finding that particles can reach breathing height from the question of how much that actually raises real infection risk — the study itself stops short of making that claim. One point the thread barely touched: regularly cleaning the bowl to cut contamination at the source is likely the more effective everyday countermeasure.
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