A standard toilet flush could be more than just flushing faeces away. Recent studies are showing that flushing can cause airborne aerosols to form that could carry micro-organisms in the bathroom air. The Science of the Total Environment has published a systematic review of 22 subjects on toilets produced aerosols.
They summarize the evidence that flushing toilets can generate bioaerosols that are transported to the adult breathing zone. They note that the quantity released is highly dependent on the amount of microbial material in the toilet and the energy of the flush.
When the toilet is flushed, the quickly moving water churns around in the bowl and causes turbulence. This churn can fragment water into tiny droplets and particles suspended in the air.
While many of these particles are sufficiently large to settle out fairly rapidly, the smaller aerosols can stay suspended and be transported throughout the bathroom.
Previous tests conducted of commercial toilets (before their design was optimized) showed that upon flushing, a turbulent air jet exceeding 2m/s was created that transported aerosols to a height of approximately 1.5m within 8seconds. The reason height is important is because it overlaps with the breathing zone of an adult when standing near.
The most recent review found that higher concentrations of microorganisms in the influent and larger quantities of flush volume was generally linked to larger aerosol and bioaerosol concentrations. These two factors, beyond flushing energy, were noted by the authors to be important determinants of potential exposure.
Which Pathogens Possabe found?
The point is not simply that every act of flushing renders every toilet a dangerous cloud of infectious disease, but whether you happen to have infectious micro-organisms in the shitter, and whether a sufficient quantities of them are aerosolized to constitute a genuine hazard.
Studies have already been done showing that aerosol from toilets can contain microorganisms that are linked to disease.
Researchers have looked at organisms such as bacteria and viruses and the discussion in these papers has referred to pathogens like influenza and norovirus.
An experimental study conducted in 2024 reported that flushing a squat toilet generated air borne microbiology and also reported that 96% of measured droplets were below 2 m in diameter.
These small droplets are more likely to suspend in indoor air than larger droplets.
Did do Closing the Toilet Lid Solve The Problem? Apparently the simple solution is not quite that simple. The review from 2026 will highlight though that there is still limited and inconsistent evidence on the independent effect of lid position.
This means that at this stage, researchers are unable to state that covering a toilet makes a complete barrier to aerosols. Various studies were conducted to determine whether aerosols could escape through the loose seat/bowl connection with the lid closed.
A 2025 study discovered that the amount of aerosols escaping through the seat/Bowl connection increased with increasing gap size.
And of course this doesn’t mean that toilet lids are pointless. Although they may prevent some material from escaping directly into the immediate environment, they are definitely not a perfect barrier.
