A toilet flush can send tiny particles into the air at adult breathing height, where they may linger for at least 20 seconds, according to new research.
The study also suggests that simply closing the lid may not fully protect people from a “plume” carrying potential pathogens.
The findings add to earlier research showing that public toilets are a hard-to-avoid reservoir of microbes.
Researchers at Flinders University examined 22 studies on aerosols produced by toilet flushing, with their review published in the journal Science of the Total Environment.
They found that microbes present in flushing water, or introduced through contamination in the toilet bowl, can become airborne as aerosols. More turbulent flushes were linked to the release of greater numbers of particles.
Among those particles are bioaerosols — airborne droplets or particles containing biological material — which can carry pathogens such as legionella, influenza and norovirus. Evidence remains mixed on whether Covid can spread through toilet-generated aerosols.
The review found that higher aerosol levels in toilet water and greater turbulence during flushing increased the amount of material suspended in the air. However, the researchers said the influence of bathroom ventilation and whether the lid was open or closed was less clear.
Even so, lead author and PhD student Lira Adiyani said she would still advise people to close the lid after using the toilet.
“Toilet flushing creates turbulence that can release aerosols into the surrounding air,” she said.
“Some studies detected these aerosols at adult breathing height, indicating a potential pathway for inhalation exposure.
“The more microbes present in the toilet, the more bioaerosols may be released. Therefore, larger flush volumes generally produce more aerosols.”
Adiyani said “based on the available evidence” she would still recommend closing the lid as a precautionary measure, “while recognising that it does not completely prevent aerosols from escaping”.
In the report, the researchers wrote that the effects of indoor aerosols had been “understudied” despite the risk of infection. This had “important implications for risk assessment, building design, and infection control in an era of water security pressures and emerging infectious diseases”, they wrote.
“Indoor aerosols influence air quality and human health as their small size allows them to penetrate deep into the respiratory tract when inhaled, providing a direct exposure pathway.”
Co-author, environmental health professor Harriet Whiley, said people didn’t have to be worried in their own homes, unless someone in the house was immunocompromised.
She said the team was working on “protecting the most vulnerable through good design” in places such as hospitals and aged care environments.
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They are increasingly concerned about “opportunistic pathogens” that can be present in water, particularly recycled or rainwater. “They don’t affect healthy people,” she said. “But if you’re immunocompromised you can get very sick, and it can be fatal.”
So it’s about getting “an effective flush with less volume and less turbulence”, she said.
Dr Lotti Tajouri, an associate professor in molecular genetics at Bond and Murdoch universities wasn’t involved in the research but warned bathroom dangers go well beyond the toilet.
His own research is particularly focused on public toilets and mobile phone use in toilets.
“As soon as you enter a toilet, consider everything contaminated,” he said.
The door will have microbes on it, as will the floor – so you should never put anything on it, he said. Then you might touch the lid, after which you flush with the lid up or down.
If it’s up, you get the “plume” effect, an “explosion or aerosols … you are literally sprayed [with]”.
Flushing with the lid down might limit your exposure to the plume, but depending on the cleanliness of the toilet, previous users have left microorganisms on every surface anyway. “The roof, the walls, the floor,” he said.
Then, you touch the toilet door again, before (hopefully) washing your hands. But you will probably touch the taps again, blow microorganisms around with the hairdryer, touch the exit door and then touch your phone.
“Studies show between 50% and 80% of people use mobile phones in the toilet. For younger generations it’s almost 100%,” he said. “They will contaminate their phones and fingers with fecal microorganisms – salmonella, campylobacter, all sorts of bacteria and viruses.
“The less contact you have, the better it is.”
