Flushing the toilet might be a lot grosser than you expected.
According to scientists, flushing emits “toilet plumes” of tiny droplets that spread through the air to every surface in the bathroom.
But can closing the lid protect you from this spray?
Unfortunately, scientists at the University of Arizona say it doesn't actually make a difference whether the lid is up or down.
Instead, regularly cleaning the bowl with disinfectant can eliminate the worst bacteria and make flushing safe regardless of the lid's position, they say.
Scientists say flushing can release a cloud of aerosolized bacteria and viruses into the air – but is it better to leave the lid open or closed while flushing?
It has been known since the 1950s that flushing the toilet results in an explosion of feces, toilet water, and anything else that might be in the toilet.
But it also includes material you can't see, as scientists say “toilet plumes” contain droplets so small they form an invisible aerosol mist.
Previous University of Colorado studies using green lights and lasers have shown that these clouds can fly 4.9 feet above the toilet in eight seconds.
What's even more concerning is that these aerosols can travel through air currents and carry bacteria and viruses throughout the bathroom, covering all surfaces and people present.
This can lead to the spread of diseases such as E. Coli, Norovirus and even Covid 19.
Due to the associated risk of infection, particularly in hospital wards or in immunocompromised individuals, prevailing opinion recommends closing the lid to store the spray.
But as the researchers emphasize in their work, this has no substantial scientific basis.
They say in their article published in the American Journal of Infection Control: “The potential benefit of closing the toilet lid while flushing in reducing viral contamination of toilet surfaces has not been empirically demonstrated.”
Researchers colonized a toilet with MS2 bacteria, a model for E. Coli, and took samples from the areas around the toilet one minute after flushing
The most contaminated areas of the bathroom after flushing:
Source: M. Goforth et al., 2024
To find out more, the researchers populated a public and private toilet with samples of MS2 bacteria as a model for E. Coli.
The toilets were then flushed and after one minute samples were taken from various surfaces around the bathroom.
These samples were then taken to the laboratory and examined to determine how contaminated they were.
What was surprising was that there was no statistically significant difference between closing the lid and not closing it.
The researchers found that samples taken from around the toilet appeared to be equally contaminated with MS2 regardless of whether the lid was open or closed.
Instead, the researchers found evidence that closing the lid likely changed the cloud's trajectory—down toward the ground rather than straight up into the air.
Overall, the toilet seat, both top and bottom, was the most contaminated area, followed by the floor around the toilet and the walls on either side.
However, the toilet lid itself seemed to stay strangely clean.
Surprisingly, the researchers found that opening or closing the lid made no statistically significant difference in the spread of bacteria in the bathroom
The researchers wrote: “Surprisingly, MS2 contamination of the bottom and top of the toilet lid was consistently low, regardless of the position of the lid before flushing.”
The public toilets in the study, which do not have a lid to close, were consistently more contaminated than the home toilet.
However, researchers suspect this is likely due to the higher flow of water into the toilet bowl when flushing in public toilets.
Still, there's no reason to be afraid of flushing toilets because researchers believe there is a solution.
The scientists examined how bacteria spread during routine toilet cleaning with and without the use of disinfectants.
They found that cleaning with the brush alone spread MS2 bacteria to the brush, toilet brush holder and parts of the surrounding area.
But vigorous brushing in addition to the addition of disinfectants reduced toilet water contamination by 99.99 percent compared to brushing alone.
Adding Lysol disinfectant to the bowl before flushing also statistically significantly reduced the contamination of the brush used to clean the toilet.
While the disinfectant did not prevent some aerosolized bacteria from spreading throughout the bathroom as a result of cleaning, it did significantly reduce the amount of bacteria remaining in the bowl.
But as this graphic shows, adding disinfectant to the toilet bowl during cleaning resulted in a significant reduction in the amount of bacteria in the bowl. It is important to note that the scale in this graph is logarithmic, not linear, so differences may appear less significant than they actually are
This is important because researchers note that bacteria can remain in the toilet even after multiple flushes.
For example, if you share a bathroom with someone who has norovirus, you could contract the disease through flushing, even if you don't go to the bathroom right after the person
But given the significant impact of disinfectants on bacteria levels in water, researchers say regular toilet disinfection is the best way to minimize this risk.
The use of disinfectants is particularly important if a household member's immune system is weakened.
Although the researchers note that the contamination levels found in this study were relatively low, they claim this shows that douching is a potential route of infection.
They therefore recommend regular disinfection of all toilet surfaces after toilet brushing and/or the use of a disinfectant that leaves a residual microbicidal effect.
“Especially if there is a person in the household who has an active infection with a virus such as norovirus, which causes acute gastroenteritis.”