Will flushing with the lid down prevent your bathroom from being filled with the dreaded ‘toilet plume’? Scientists test an old theory and make a very surprising discovery

Will flushing with the lid down prevent your bathroom from being filled with the dreaded ‘toilet plume’?  Scientists test an old theory and make a very surprising discovery

  • Scientists say flushing a toilet can spread a plume of bacteria and viruses
  • It reveals whether leaving the lid up or down is best to reduce contamination



Cleaning a toilet may be a lot more difficult than you expected.

According to scientists, the flow of water sends “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 from the University of Arizona say it actually makes no difference whether the lid is up or down.

Instead, cleaning the bowl regularly with disinfectant can eliminate the worst bacteria and make cleaning safe no matter where the lid is, they say.

Scientists say rinsing can release a plume of bacteria and viruses into the air, but is it better to leave the lid open or closed when rinsing?

Read more: Never flush a toilet again! Scientists say 3D-printed toilets are so slippery that nothing can leave a mark in them

Since the 1950s, it has been known that flushing a toilet causes feces, toilet water, and whatever else may be in the bowl to explode.

But this includes substances you can’t see, with scientists saying ‘toilet plumes’ contain droplets so small they form an invisible spray.

Previous studies from the University of Colorado used green light and lasers to reveal that these plumes could fly 4.9 feet above a toilet within eight seconds.

Even more worrying is that these aerosols can drift with air currents and carry bacteria and viruses around the bathroom, covering any surfaces or people present.

This can lead to the spread of diseases such as E. coli, norovirus, and even Covid-19.

Given the risk of infection this creates, especially in hospital wards or for immunocompromised people, prevailing wisdom recommends closing the lid to contain the droplets.

But as the researchers point out in their paper, this has no substantive scientific basis.

“The potential benefit of closing the toilet lid during flushing to reduce viral contamination of bathroom surfaces has not been experimentally proven,” they say in their research published in the American Journal of Infection Control.

The researchers cultured MS2 bacteria in the toilet, a model of E. Coli, and took samples from the areas surrounding the toilet one minute after flushing.

The most polluted areas of the bathroom after cleaning:

  1. Toilet bowl water
  2. Toilet brush
  3. Toilet seat (upper and lower)
  4. The floor surrounding the toilet
  5. Bathroom walls
  6. Toilet cover

Source: M. Goforth et al

To learn more, the researchers cultured samples of MS2 bacteria in a public and private toilet as a model for E. Coli bacteria.

The toilets were then flushed, and after a minute samples were taken from various surfaces surrounding the bathroom.

These samples were then transported to the laboratory and studied to determine the extent of their contamination.

Surprisingly, there was no statistically significant difference between closing the lid or 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 up or down.

Instead, the researchers found evidence that closing the lid likely changed the plume’s path — down toward the ground rather than straight up into the air.

In general, the toilet seat was the most contaminated area, top and bottom, followed by the floor surrounding the toilet, and the walls on both sides.

However, the toilet lid itself seems to remain strangely clean.

Surprisingly, the researchers found that leaving the lid open or closed did not make a statistically significant difference in the spread of bacteria around the bathroom

Read more Aerosol droplets from bathrooms containing urine, faeces and vomit remain in the air for up to 20 seconds

Harpic Chemicals used specialized high-speed cameras to capture the explosion of particles from a toilet

“Surprisingly, MS2 contamination at the bottom or top of the toilet lid was consistently low, regardless of the position of the lid before flushing,” the researchers wrote.

The public toilets in the study, which do not have a closing lid, were found to be consistently more polluted than home toilets.

But researchers point out that this is likely due to higher water flow into the toilet bowl during flushing in public toilets.

But there is still no reason to be afraid of using a toilet flush, as researchers believe there is a solution.

Scientists tested how bacteria spread during routine cleaning of toilets with and without disinfectants.

They found that brushing alone spread MS2 bacteria to the brush, the toilet brush caddy, and parts of the surrounding area.

But vigorous brushing plus the addition of disinfectant reduced toilet water contamination by 99.99 percent compared to brushing alone.

Adding Lysol disinfectant to the bowl before flushing also resulted in a statistically significant reduction in contamination of the brush used to clean the toilet.

While the sanitizer did not prevent the cleaning from spreading some of the bacteria flying around the bathroom, it did significantly reduce the amount of bacteria remaining in the bowl.

But, as this graph shows, adding disinfectant to the toilet bowl during flushing 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 rather than linear, so the differences may appear less significant than they actually are

Read more: Royal flush! Stylish new smart toilets that operate with hand gestures and Alexa from Amazon

This is important because the researchers noted that bacteria can remain in the toilet even after frequent flushing.

If you share a bathroom with someone who has norovirus, for example, you may get sick by flushing the toilet even if you don’t use the toilet immediately afterward.

However, given the significant impact of disinfectant on bacteria levels in water, researchers say that regularly disinfecting the toilet is the best way to reduce these risks.

Using a disinfectant is especially important when a family member has a weakened immune system.

Although the researchers note that the contamination levels found in this study were relatively low, they stress that this indicates that cleaning is a potential route of infection.

They therefore recommend “regular disinfection of all bathroom surfaces after flushing the toilet, and/or the use of a disinfectant that leaves a residual microbicidal activity.”

“Especially when the home is occupied by an individual with an active infection with a virus, such as norovirus, causing acute gastroenteritis.”

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