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Microbiologist’s toilet experiment shows just how much bacteria enters the air every time we flush

Leaving the toilet seat up or down after leaving the bathroom has always been a great debate between couples. But what about closing the lid versus leaving it up before you flush?

Recently, a microbiologist set out to answer this question once and for all and later shared his findings on TikTok so others could benefit from them, too.

“When you flush your toilet, aerosol is sprayed into the air,” explains TikTok user What Might Grow (@whatmightgrow) in the now-viral video.

But the real question, he continues, is just how much bacteria actually comes along for the ride.

To get to the bottom of it, the unnamed microbiologist found a public restroom toilet with a high-powered flush. As he admits in the clip, he left a “no. 2” in the toilet and placed a petri dish balancing on the back of the toilet for 10 minutes before flushing. Then, he placed another petri dish on the back of the toilet and proceeded to flush.

The objective was to see how much bacterial growth (if any) would appear in each petri dish over time, and after waiting patiently, he finally began to see a difference.

In the petri dish left out for 10 minutes without flushing the toilet, the scientist saw no noteworthy bacteria growth. However, in the second dish — which was left out as he flushed the toilet — he watched as two circular growths began to get bigger and bigger, proving that flushing does, in fact, release bacteria into the air around us.

That said, @whatmightgrow admitted to being “not impressed” by how little bacteria growth was really present, vowing to recreate the experiment another time on a different, dirtier toilet.

Just a few days later, he was back again to share his findings.

Here, he tested out his own home toilet compared to a public toilet that seemed dirtier than the first.

This time, he let the bacteria grow over a five-day period and hoped to get a more definitive answer. But yet again, he says he was surprised that not much bacteria grew.

“You guys, I didn’t want to walk away without confirming your fears about bathroom flushes, so I ended up flushing five times during those 10 minutes.”

After looking at the petri dish, he could see there was “crap in it,” but not that much bacterial growth. The others had a little bit more but nothing to write home about.

In other words: There were no big shockers here.

“It appears to be not as gross as I, and probably you, originally believed,” the scientist concluded. “Sorry to disappoint.”

In the comments, people were actually relieved to hear this news.

“No disappointed at all!” one person wrote. “Surprised, but not disappointed.”

“Such a relief because my hubby keeps forgetting to cover it,” added someone else. “Phew.”

Other TikTokers said they started closing the lid for other reasons anyway.

“I put the lid down because my cat would put her paws in the bowl and drink the water,” one woman shared.

“I put the seat down cause i hate fishing out stuff that falls in,” another admitted.

In the end, even though the TikTok was pretty compelling, most people said they would still stick to closing their toilet lid.

“The seat still goes down,” one person wrote. “I’ve come too far in this argument with my husband to recoil now.”

“Oh thank god,” said someone else. “I saw that vid of the spray and have been putting the seat down since so I don’t live in a Petri dish. Good to know it’s not that bad.”

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