Few people go out of their way to touch a toilet. When we inevitably must, it’s advisable to always wash your hands afterward, even if the toilet looks clean.
That’s because a toilet’s daily duties tend to leave it teeming with microbes, including potentially dangerous bacteria and viruses. If you leave those germs on your hands, you could sicken yourself and others.
As a new research review highlights, however, washing your hands may not always be enough.
Flushing a toilet produces an upward plume of unsavory aerosols, which can rise into the breathing zone of adults and persist there for 20 seconds.
This plume could hold a wide array of microbial passengers, as previous research has shown, and seems capable of ferrying pathogens directly onto people or onto surfaces we might touch.
Yet while many studies have demonstrated the existence of such plumes, and examined their contents and behavior, the evidence so far is still “fragmented and highly variable,” the authors of the new review write.
Previous studies vary in experiment design, measurement methods, target microbes, and reporting, the researchers note, and have not consistently accounted for plume-influencing factors like bathroom ventilation or the physical and hydraulic characteristics of toilets.
Given what we do know about toilet germs and flush plumes, this phenomenon seems worth learning more about. It could already pose a hazard in places like hospitals, where many patients are more vulnerable to infection, and may play a wider role in some disease outbreaks.
In hopes of learning more, researchers from Australia conducted a systematic literature review, analyzing 22 studies of toilet-generated aerosols.
“Toilet flushing creates turbulence that can release aerosols into the surrounding air,” says lead author Lira Adiyani from Flinders University.
“Some studies detected these aerosols at adult breathing height, indicating a potential pathway for inhalation exposure.”
Although the plumes are largely water, they can also feature bioaerosols – airborne particles arising from biological sources. Many of these are whole bacteria or viruses, and some can run amok inside a human nose or mouth.
The danger depends on a variety of factors, Adiyani says, such as the volume and energy of a flush as well as a toilet’s abundance of pathogenic microbes.
“The microbes can originate both from contamination of the toilet bowl during use, or from the water used for flushing,” she says.
“The more microbes present in the toilet, the more bioaerosols may be released. Therefore, larger flush volumes generally produce more aerosols.”
The review included some studies in which researchers first “seeded” toilet water with microbes or fluorescent surrogate particles, as well as others conducted under more natural conditions.
Aerosol levels differed significantly among studies, the review found, depending on various experimental conditions, toilet properties, and sampling techniques.
In studies that involved seeding toilet water, higher concentrations of microbes in a toilet corresponded with higher concentrations of bioaerosols in its flush plume. Higher bioaerosol levels were often found closer to the toilet seat.
This points to the importance of toilet hygiene, Adiyani and her colleagues note. Regularly cleaning a toilet and nearby surfaces can curb microbial growth, which seems to reduce the prevalence of bioaerosols after you flush.
The details of that flush matter, too, with forceful, high-volume flushes launching more microbes. This suggests we might limit bioaerosols by choosing toilets with lower flush volumes, or at least those with a lower-volume option.
The review did not find significant associations between aerosol levels and ventilation or lid position, but these are likely still worthwhile precautions, the authors say, as they could influence how aerosols move within a bathroom.
Related: Gross Toilet Flushes Really Could Spray Viral Particles in The Air, Study Finds
While ventilation may help disperse aerosols, some findings suggest closing the toilet lid can obstruct their ascent in the first place. A closed lid didn’t seem to stop the plume entirely, but it did redirect aerosols outward through gaps between the lid and seat instead of sending them up.
“Based on the available evidence, I would recommend closing the toilet lid before flushing, where a lid is available, as a precautionary measure to minimize potential inhalation exposure – while recognizing that it does not completely prevent aerosols from escaping,” Adiyani says.
This review helps shed light on toilet aerosols, but there’s still plenty we don’t know about how the plumes work and how to limit them, says environmental microbiologist Harriet Whiley, a professor at Flinders University and co-author of the review.
“Further research is needed to develop design and engineering interventions that reduce toilet-generated bioaerosols, particularly in high-risk settings such as hospitals,” Whiley says.
The study was published in Science of the Total Environment.
This article was fact-checked by Rachel Garner and edited by Peter Dockrill. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
