Flushing toilets aerosolizes pathogens that reach adult breathing heights and remain airborne for at least 20 seconds. Flinders University researchers reviewed 22 studies, publishing results in the Science of the Total Environment, revealing that closing the lid alters dispersion but does not stop it.
How Toilet Flushing Launches Pathogenic Aerosols Into the Air
Public and private restrooms harbor invisible contamination that turns an everyday bathroom habit into an inhalation risk. Flinders University researchers systematically analyzed 22 studies examining aerosol and bioaerosol generation during toilet flushes, publishing their findings in the Science of the Total Environment journal. High-velocity flush water creates turbulence inside the bowl, shearing liquids into tiny droplets that hang in the surrounding air. The review analysed 22 studies of toilet-generated aerosols, including studies using microorganisms or surrogate organisms seeded into toilet water as well as studies conducted under normal, unseeded conditions.
Lead author and PhD student Lira Adiyani explained the physical mechanics during the flush cycle. 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.
Furthermore, the investigation determined that microbes can originate from both the water used for flushing and the contamination of the toilet bowl during use. The more microbes present in the toilet, the more bioaerosols may be released. Therefore, larger flush volumes generally produce more aerosols,
Ms Adiyani noted.
The resulting bioaerosols are capable of carrying biological material that transmits serious pathogens, including legionella, influenza, and norovirus. There are differing reports about whether Covid spreads through toilet aerosols. Among experiments where microorganisms were deliberately introduced into toilet water, higher microbial concentrations in the water were associated with higher concentrations detected in aerosols. Higher aerosol concentrations were also commonly reported closer to the toilet, particularly around seat height. Aerosols were reported to remain suspended in the air for at least 20 seconds after flushing.
The Limitations of Closing the Toilet Lid
While closing the lid is a common reflex, researchers found that it might not be enough to avoid a plume of potential pathogens. Although ventilation and lid position were not significantly associated with aerosol concentrations in the review, they may still influence how aerosols disperse within the bathroom. Evidence from individual studies suggests that closing the lid can alter the direction of aerosol dispersion, with aerosols escaping through gaps between the lid and toilet bowl rather than travelling directly upwards.
Despite these findings, Ms Adiyani maintains that the practice remains a sensible precaution. “Based on the available evidence, I would recommend closing the toilet lid before flushing, where a lid is available, as a precautionary measure to minimise potential inhalation exposure – while recognising that it does not completely prevent aerosols from escaping,” she stated.
Broader Bathroom Risks and Vulnerable Populations
The implications of the research extend to broader facility engineering, building design, and infection control, particularly in an era of water security pressures and emerging infectious diseases. 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. In the report, the researchers wrote that the effects of indoor aerosols had been understudied despite the risk of infection.
Research co-author Professor Harriet Whiley, from Flinders University’s College of Science and Engineering, emphasizes that everyday people do not need to panic inside their personal residences. You don’t have to be worried in your own home, unless someone in the house is immunocompromised, she explained. Instead, her team is actively working on protecting the most vulnerable through good design
in high-risk environments such as hospitals and aged care facilities. 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.
Professor Whiley suggested focusing on getting an effective flush with less volume and less turbulence, noting that choosing toilets designed with lower flush volumes, or using the lower-volume option on dual-flush toilets where appropriate, may help minimise aerosol production.
Dr Lotti Tajouri, an associate professor in molecular genetics at Bond and Murdoch universities who was not involved in the research, issued broader warnings regarding total restroom hygiene. As soon as you enter a toilet, consider everything contaminated,
he said, pointing out that doors and floors carry microbes and that mobile phone usage inside restrooms compounds the hazard. If the lid is up during a flush, users face an explosion of aerosols, meaning they are literally sprayed. Even with the lid down, previous users may have left microorganisms on every surface.
Together, these findings suggest that maintaining good toilet hygiene, including regular cleaning of the toilet and surrounding surfaces, and handwashing after use may help minimise microbial contamination and potential exposure to microbial disease. Adequate ventilation may also help disperse and remove suspended airborne particles.
