Rumors have circulated that flushing with the lid open may splash toilet water onto nearby objects, including toothbrushes. Distinguishing myth from evidence is essential, which prompted a research team at the University of Arizona to systematically investigate the issue. Their study, published in the American Journal of Infection Control, examined how flushing with the lid up affects contamination of surrounding bathroom surfaces and yielded surprising findings.
Earlier research documented that bacterial aerosols can be generated during a toilet flush. The 2024 study extends these findings to viral agents, confirming that viruses are also aerosolized. Crucially, the investigators found that closing the lid before flushing does not substantially reduce the dispersal of viral particles. They explained that gaps around the seat allow aerosolized droplets to escape, limiting the lid’s protective effect.
The study also revealed that cleaning the bowl with a standard toilet brush, absent a disinfectant, fails to curb contaminant spread. Effective cleaning requires disinfectants to neutralize fecal bacteria before they can contaminate adjacent surfaces. Unlike the controlled environment of space, terrestrial toilets release aerosolized particles into the bathroom air during flushing, potentially depositing them on nearby items. Consequently, storing toothbrushes and other personal items out of the bathroom vicinity remains prudent.
While the data indicate that lid closure does not dramatically curb particle dispersion, it does alter the trajectory of the aerosol plume. Lowering the lid reduces the vertical component of the spray, redirecting droplets downward rather than upward. Thus, although pathogens may still be airborne, the lid helps keep them from dispersing directly into the room’s upper airspace.
Bacteria can be remarkably hardy, and viruses, due to their sub‑micron size, travel more easily in fine droplets. This explains why a closed lid alone cannot fully prevent aerosolization, yet it remains a valuable hygiene measure. Reducing aerosol spread is especially important for organisms that resist conventional decontamination.
The primary route for infection from toilet aerosols is inhalation for viruses and ingestion for bacteria. Although aerosolized droplets can land on surfaces, the likelihood of these pathogens entering the body through normal bathroom use is low. Keeping personal items such as toothbrushes and contact lenses out of the bathroom airspace further reduces risk.
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