Flushing toilets releases bioaerosols that reach adult breathing height and remain suspended for at least 20 seconds, according to a systematic review published in Science of the Total Environment. Researchers at Flinders University evaluated 22 studies and found that larger flush volumes and higher microbial contamination increase the release of airborne pathogens.
Flinders University Researchers Review 22 Studies on Toilet Aerosols
When a toilet flushes, the mechanical action generates a turbulent plume of particles capable of carrying microorganisms into the surrounding air. A team of researchers at Flinders University examined this phenomenon by systematically reviewing 22 studies covering toilet-generated aerosols and bioaerosols. The findings were published in the Science of the Total Environment journal.
The review encompassed experiments using both unseeded conditions and scenarios where microorganisms or surrogate organisms were deliberately introduced into the water. Investigators analyzed how varying toilet characteristics, experimental setups, and sampling methods influenced the concentration and dispersion of airborne particles. The analysis confirmed that toilet flushing acts as a direct vector for aerosol generation.
“Toilet flushing creates turbulence that can release aerosols into the surrounding air. Some studies detected these aerosols at adult breathing height, indicating a potential pathway for inhalation exposure.”
Lira Adiyani, PhD student and lead author at Flinders University
Pathogens, Turbulence, and Flush Volume Dynamics
The volume of water used in a flush and the degree of turbulence created directly dictate the volume of particles suspended. According to the data evaluated in the review, higher microbial concentrations in the bowl—originating either from flush water or previous contamination—correlate with higher counts of released bioaerosols.
These bioaerosols are capable of transmitting pathogens including legionella, influenza, and norovirus. While reports differ regarding whether Covid-19 transmits through toilet aerosols, the reviewed studies established that these airborne particles remain suspended for at least 20 seconds after the flush cycle concludes. Researchers also noted that aerosol concentrations were typically densest closest to the fixture, particularly around seat height.
Evaluating Precautionary Measures and Environmental Controls
Mitigating exposure requires practical engineering and behavioral adjustments. While the review noted that the direct impacts of bathroom ventilation and lid position were not uniformly clear across all analyzed papers, individual studies suggest that closing the lid alters the direction of aerosol dispersion, forcing particles through gaps between the lid and the bowl rather than travelling directly upwards.
“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.”
Lira Adiyani, lead author
Beyond lid habits, the study points to fixture design as a critical variable. Optimizing bathrooms for water security while controlling infection risks points toward an effective flush with less volume and less turbulence.
Vulnerable Populations and High-Risk Healthcare Settings
For healthy individuals, everyday bathroom aerosols rarely pose a severe threat. However, environmental health experts emphasize that the risk profile changes dramatically for vulnerable groups, particularly in institutional environments.
“They don’t affect healthy people, but if you’re immunocompromised you can get very sick, and it can be fatal.”
Professor Harriet Whiley, co-author and environmental health professor at Flinders University
Researchers are focusing on engineering interventions in high-risk settings such as hospitals and aged care facilities. This includes managing opportunistic pathogens found in recycled water or rainwater supplies, balancing water conservation mandates with strict infection control.
Public Restrooms and Contaminated Surfaces Beyond the Bowl
Bathroom contamination extends well past the toilet bowl itself. Dr. Lotti Tajouri, an associate professor in molecular genetics at Bond and Murdoch universities who was not involved in the Flinders University review, notes that public facilities present compounding vectors for microbial exposure.
Door handles, floors, taps, and air dryers harbor microorganisms left behind by previous occupants. Compounding this environment is the widespread use of personal electronics in restrooms. Studies cited by Dr. Tajouri indicate that between 50% and 80% of individuals—and nearly 100% of younger generations—use mobile phones in the toilet, directly transferring fecal microorganisms such as salmonella and campylobacter onto their devices and fingers.
