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What Happens When You Flush With the Lid Up?
In Short
Flushing creates a fine spray of tiny droplets that rises out of the bowl. How much of it ends up in the bathroom depends on the toilet and the flush. Closing the lid before flushing probably holds some of it back, though that isn't clearly proven. Either way, it costs nothing.
What We've Been Sold as Normal
That the flush sends everything down and that's the end of it. Most of it does go down. A small, invisible part goes up.
The Honest Explanation
What happens. When water shoots into the bowl with force, it carries the finest droplets with it, which rise as a mist. You can't see any of it with the naked eye.
How far it gets. In 2022, researchers at the University of Colorado Boulder made this mist visible with lasers. With the lidless toilet they studied, it rose to about one and a half meters within a few seconds. That was a powerful pressure-valve flush of the kind common in US public restrooms – a German cistern flushes more gently. But a mist forms there too.
What it can carry. Germs from the bowl can get into the air along with the water. How big the health risk really is in everyday life isn't well studied. For healthy people in their own bathroom it's probably small – but it's still an unnecessary route for germs.
What helps. Close the lid before flushing. That probably holds back part of the mist, even if droplets can escape through gaps. A 2024 study, however, found hardly fewer germs on bathroom surfaces with the lid closed. Don't keep toothbrushes right next to the toilet. And clean the toilet regularly – what isn't in the bowl can't end up in the air.
What You Often Hear – and What's True
“With the lid closed, nothing gets out.”
No. Some still escapes through gaps, and how much the lid really helps isn't clearly proven.
“That only applies to public toilets.”
A mist forms with every flush. Lidless public toilets with a strong flush are just the most obvious example.
“A toothbrush in the bathroom is gross.”
An exaggeration. A bit of distance from the toilet and a cup with air to dry in are enough.
“It'll make you sick.”
That isn't proven. It's an avoidable route, not a demonstrated risk.
Putting It in Context
Every flush sends a little bit of toilet into the air. That's no cause for alarm, but it's a good reason for a habit that costs nothing: lid down first, then flush. Whether it helps much is open; it does no harm.
