Will flushing with the lid down stop your bathroom being peppered with the dreaded ‘toilet plume’? Scientists test age-old theory and make a very surprising discovery

Flushing the toilet can be a lot worse than you expected.

According to scientists, flushing sends out ‘toilet plumes’ of tiny droplets that spread through the air to every surface of the bathroom.

But can closing the lid keep you safe from this spray?

Unfortunately, scientists from the University of Arizona say that it really doesn’t make any difference whether the lid is up or the lid is down.

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

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

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

Since the 1950s, it has been common knowledge that flushing the toilet results in an explosion of faecal matter, toilet water and anything else that may be in the bowl.

But that includes material you can’t see, as scientists say ‘toilet plumes’ contain droplets so small they form an invisible aerosol.

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

What’s even more concerning is that these aerosols can float on air currents and carry bacteria and viruses into the bathroom, coating any surfaces and people present.

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

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

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

They say in their paper published in the American Journal of Infection Control: ‘The potential benefit of closing the toilet lid during flushing to reduce viral contamination of toilet surfaces has not been empirically demonstrated.’

Researchers seeded a toilet with MS2 bacteria, a model for E. Coli, and sampled the areas around the toilet one minute after flushing

Researchers seeded a toilet with MS2 bacteria, a model for E. Coli, and sampled the areas around the toilet one minute after flushing

The most contaminated areas of the bathroom after rinsing:

  1. Toilet Bowl Water
  2. Toilet brush
  3. Toilet seat (top and bottom)
  4. Floor around the toilet
  5. Bathroom walls
  6. Toilet lid

Source: M. Goforth et al., 2024

To find out more, the researchers seeded a public and private toilet with samples of MS2 bacteria as a model for E. Coli.

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

These samples were then transferred to the laboratory and studied to see how infected they had become.

What was surprising was that there was no statistically significant difference between closing the lid or not.

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 trajectory of the plume — down toward the floor rather than straight up into the air.

In general, the toilet seat was the most contaminated area, top and bottom, followed by the floor around the toilet, and the walls on either side.

However, it turned out that the toilet lid itself remained strangely clean.

Surprisingly, the researchers found that leaving the lid open or closed made no statistically significant difference to the spread of bacteria in the bathroom.

Surprisingly, the researchers found that leaving the lid open or closed made no statistically significant difference to the spread of bacteria in the bathroom.

The researchers wrote: ‘Surprisingly, MS2 contamination from the bottom or top of the toilet lid was consistently low regardless of lid position before flushing.’

The public toilets in the study, which do not have a lid to close, were found to be consistently more contaminated than the domestic toilet.

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

But there’s still no reason to fear flushing your toilet, as the researchers believe there is a solution.

The scientists tested how bacteria were spread during routine toilet cleaning with and without the use of disinfectant.

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 disinfectant reduced toilet water contamination by 99.99 percent compared to brushing alone.

Adding Lysol disinfectant to the bowl before flushing also saw statistically significant reductions in the contamination of the brush used to clean the toilet.

Although disinfectant did not stop cleaning from dispersing some aerosolized bacteria in the bathroom, it did significantly reduce the amount of bacteria left in the bowl.

But, as this graph shows, adding disinfectant to the toilet bowl during cleaning resulted in significant reductions in the amount of bacteria in the bowl.  It is important to note that the scale on this graph is logarithmic rather than linear, so differences may appear less significant than they actually are

But, as this graph shows, adding disinfectant to the toilet bowl during cleaning resulted in significant reductions in the amount of bacteria in the bowl. It is important to note that the scale on this graph is logarithmic rather than linear, so differences may appear less significant than they actually are

This is important because the researchers note that bacteria can linger in the toilet even after several flushes.

For example, if you share a bathroom with someone who has norovirus, you can become infected with their disease by flushing, even if you don’t use the toilet directly after them.

Still, given the significant effect of disinfectant on levels of bacteria in the water, the researchers say that regular toilet disinfection is the best way to reduce this risk.

The use of disinfectant is especially important when a member of the household has a compromised immune system.

Although the researchers note that the levels of contamination found in this study were relatively low, they maintain that this shows that flushing 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 residual microbial activity.

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