Flushing a toilet releases an invisible plume of microscopic droplets containing bacteria, viruses, and fecal matter into the air, a phenomenon that could pose a health risk, according to a review of existing research.
Researchers from Flinders University analyzed 22 studies that investigated the aerosols generated by flushing toilets. The findings indicate that these particles can travel significant distances and remain airborne long enough to be inhaled.
Some studies included in the review detected particles more than five feet above the floor, within the breathing zone of many individuals. These airborne particles were found to persist for at least 20 seconds after a flush. The size of many of these particles ranged from 0.3 to 10 micrometers, with a majority under 3 micrometers, making them small enough to remain suspended in the air and potentially enter the respiratory system.
The amount of bacteria present in the toilet water, referred to as microbial “loading,” directly correlates with the quantity of aerosolized spray. The review found that a tenfold increase in microbial concentration in the water was associated with approximately 2.6 times more bacteria in the air. Additionally, the flushing energy, or the volume of water used in a flush, also contributes to the release of these particles, with each additional liter of water linked to roughly a 1.3-fold increase in airborne bacteria.
Visual studies have demonstrated the reach of these flush plumes. A 2022 study from the University of Colorado used a laser to visualize a commercial toilet releasing aerosols up to approximately 1.5 meters within eight seconds.
While closing the toilet lid before flushing is often recommended for hygiene, its effectiveness against these microscopic aerosols is limited. A 2024 study published in the American Journal of Infection Control indicated that closing the lid successfully trapped larger particles but did not prevent smaller, microscopic ones from escaping through gaps between the lid, seat, and bowl. The recent review also found limited evidence that the lid's position significantly altered the airborne plume.
Despite the limited impact on microscopic particles, researchers still advise closing the lid as a precautionary measure to help reduce the amount of toilet "loading" that becomes airborne. Other recommended practices to minimize germ spread include regular toilet cleaning, thorough handwashing, and utilizing the lower-volume option on dual-flush toilets where available.
While these measures are practical for private bathrooms, the implications of flush plumes are particularly concerning in public restrooms. Further research is needed to develop effective interventions for mitigating toilet-generated aerosols in these shared spaces.