The Fecal Plume: A Discovery Dating Back to the 1950s
The existence of bioaerosols generated by toilets is nothing new. The earliest experiments documenting this phenomenon date from the 1950s, but it was in 1975 that Charles Gerba, a microbiologist, truly popularized the concept of disease transmission via the toilet plume. Since then, dozens of studies have confirmed and clarified the scale of the problem.
The mechanism is simple: when water swirls in the bowl during a flush, it creates bubbles, splashes, and turbulent motion that project into the air microscopic droplets containing everything that was in the bowl. These particles, invisible to the naked eye, form a cloud that ascends rapidly out of the bowl and can reach several feet in height.
Philip Tierno, a microbiologist at New York University, asserts that these plumes can rise as high as 4.5 meters. In a typical bathroom where the toilet and sink are close to each other, your toothbrush ends up in the direct impact zone.
Numbers that Send a Cold Shiver Down Your Spine
Scientific studies on toothbrush contamination reveal alarming statistics. One study showed that 54.85% of tested toothbrushes were contaminated with fecal matter, with an 80% probability that these fecal coliforms originated from another person using the same bathroom. In other words, in a shared household you are not just dealing with your own intestinal bacteria—you are also sharing those of your roommates or family members.
The University of Manchester established that an average toothbrush can harbor more than 10 million bacteria. Among the microorganisms identified on toothbrushes stored near toilets, there are names that are hardly reassuring: Staphylococcus aureus, E. coli, Salmonella, Pseudomonas, Klebsiella, not to forget fungi like Candida and various mold spores.
The Worrying Persistence of Bioaerosols
What makes this phenomenon particularly troubling is how long these particles stay suspended. A study published in Scientific Reports measured bioaerosol concentrations at various distances and moments after a flush. The results showed that bioaerosol concentrations did not vary significantly with time or distance, suggesting that the aerosols generated can remain in suspension for more than 30 minutes after flushing.
Another study using the bacterium Clostridium difficile as a tracer recovered this bacterium in the air up to 25 centimeters above the toilet seat and up to 90 minutes after flushing, with concentrations 12 times higher when the lid was up compared to when it was down.
This means that even if you leave the bathroom immediately after flushing, the particles keep circulating and settling on nearby surfaces for an hour and a half. Your toothbrush, your towel, your makeup—anything left uncovered—becomes a potential target.
Closing the Lid Isn’t Always Enough
The solution seems obvious: lower the lid before flushing. And indeed, this greatly reduces the dispersion of larger droplets. However, a study published in January 2024 showed that viruses still escape into the plume even with the lid down.
Modern toilets equipped with powerful flushing systems, particularly those in public places with high-pressure flushes, generate even more bioaerosols than domestic low-flow models. And of course, most public toilets do not even have a lid.
How to Really Protect Your Toothbrush
The first protective measure remains to consistently close the lid before flushing. But that’s only the beginning. The storage of your toothbrush deserves special attention.
Contrary to what intuition might suggest, placing a plastic cap on your toothbrush is a bad idea. The bristles stay moist under the cap, creating an ideal environment for bacterial growth. The best option is to store your toothbrush in a vertical holder that allows air drying, but as far away from the toilet as possible.
If your layout does not allow you to move the toothbrush far enough away, consider storing it in a closed cabinet or even in another room. Some people opt for a bathroom drawer, which offers acceptable protection against direct splashes.
Rinse your toothbrush carefully before and after each use to help remove surface bacteria. Finally, follow the recommendation to replace your toothbrush every three to four months, or sooner if the bristles begin to fray.
