Toilet lids don't protect against post-flush surface germs: study

When it comes to ensuring the toilet doesn’t leave tiny particles of fecal matter all over your bathroom every time you go number two, one piece of advice has held strong: just make sure you put down the toilet lid before you flush.

However, a new study suggests closing the toilet seat may not have as big of an impact as we thought in cutting down the risk of pathogens getting on our bathroom surfaces.

The study, published last week in the peer-reviewed American Journal of Infection Control (AJIC), found that the amount of viral contamination of bathroom surfaces did not change whether the toilet seat was up or down during flushing.

“With results showing that closing toilet lids has no meaningful impact on preventing the spread of viral particles, our study highlights the importance of regular disinfection of toilets to reduce contamination and prevent the spread of viruses,” Charles P. Gerba, professor of virology at the University of Arizona and senior author of this study, said in a press release.

He added that the findings are most concerning for health-care settings, where potential pathogens pose a higher risk to immunocompromised patients who might be immunocompromised. It's important to note that this study did not look at airborne particles, only those that settle on surfaces.

In order to measure the toilet lid’s effect, researchers took a surrogate for the kind of gastrointestinal bacteria that might end up in a toilet during the average visit and added that to the toilet water. Then, they tested how far it could spread when the toilet was flushed with the lid up or down.

Two different types of toilet sold in the U.S. were used, including a public toilet located in the public restroom of an office building and a toilet in a residential home. The surrogate was not a human or animal pathogen, so no protective clothing was required, the study says.

Researchers recorded the amount of bacteria that settled on surfaces in the bathroom around one minute after each test flush.

Whether the toilet was flushed with the lid up or down, there was no statistical difference between the amount of viral material found on the floor or toilet seat, researchers found.

There was minimal contamination of the walls in all scenarios.

However, a second analysis, in which researchers looked at how effective it was to clean the toilet with or without disinfectant, showed that cleaning the toilet bowl with disinfectant and a toilet brush significantly reduced the amount of virus present in the toilet.

“(This study) underscores the importance of regular disinfection of surfaces in healthcare settings for reducing the spread of viral infections,” Tania Bubb, 2024 president of AJIC, said in the press release.

So should we completely forego putting the toilet seat down to flush? Probably not, according to existing research.

This study only looked at surfaces, but a 2022 study, for instance, found that flushing the toilet with the seat open created a huge amount of airborne particles that could linger in the air for minutes—which is definitely not something anyone would want to inhale.