Toilets and Toothbrush Issues

Modern sanitation is a luxury for much of the world: with a simple flush, our waste disappears. ⁽¹⁾

With the press of a handle and a powerful whoosh of water, toilets send waste far away from humans and down into the sewer system. But research shows in surprising detail just how much waste they also spew into the air, potentially spreading contagious diseases in the process. ⁽²⁾

Using lasers and cameras, scientists visualized the plume of tiny, aerosolized particles ejected from commercial toilets during flushing. During experiments using continuous and pulsed lasers, airborne particles ejected from the toilet traveled at speeds of up to 6.6 feet per second and reached 4.9 feet above the toilet within eight seconds. And, once airborne, smaller particles measuring less than 5 microns hung in the air for more than a minute. ⁽³⁾

Public Toilets

With public toilets the truth is surprising. While bacteria can indeed be detected on the toilet seat, the risk of transmission is negligible. Our skin is a robust barrier that reliably keeps most germs away, especially when there are no open wounds.

Public toilet seats often have fewer microbes than other locations in public toilets such as door handles, faucet knobs and toilet flush levers. These parts are touched a lot more often with unwashed hands. ⁽⁴⁾

Public toilets in busy places are used hundreds or even thousands of times each week. Some are cleaned often, but others (such as those in parks or bus stops) may only be cleaned once a day or much less, so germs can build up quickly. The red flags that a toilet hasn’t been cleaned are the smell or urine, soiled floors and what is obvious to your eyes. However, the biggest problem isn’t just sitting: it’s what happens when toilets are flushed. When you flush without a lid, a toilet plume shoots tiny droplets into the air. These droplets can contain bacteria and viruses from the toilet bowl and travel up to 2 meters.

Hand dryers blowing air can also spread germs if people don’t wash properly. As well as drying your hands, you might be blowing germs all over that travel up to 2 meters. ⁽⁴⁾

Toothbrushes

Bacteria from our toilets, the cold sore veins, and thrush-causing yeast can thrive on our toothbrushes. ⁽⁵⁾

Right now, your toothbrush is home to something like 1-12 million bacteria and fungi belonging to hundreds of different species, alongside countless viruses. They form biological films on the exposed surfaces of your brush, or worm their way into the fractured stalks of ageing bristles. A daily influx of water, saliva, skin cells and traces of food from our mouths give these microbes all they need to thrive. Every so often, they are joined by a shower of other microorganisms that arrive with the flush of a nearby toilet or opening of a window.

So, should you be concerned about how clean your toothbrush is? It’s a question that has been troubling dentists and doctors for years, prompting them to examine just what is living on our toothbrushes, what risks those microbes pose and how we should be cleaning our tooth-scrubbing implements.

In most cases the risk from pathogens is small, but it could be more of a concern for those whose immune systems are compromised, meaning they are more prone to infections.

Allowing you toothbrush simply to air dry at room temperature in an upright position after use can be a simple way of reducing the microbes living there.

The American Dental Association also recommends not covering toothbrush heads or storing them in closed containers as this can encourage microbial growth. ⁽⁵⁾

Your toothbrush is affected by repeated exposure to toothpaste, food particles, and saliva. It’s also subjected to daily re-inoculation from the user’s mouth. This causes the bristles to support a thriving biofilm of oral bacteria that comes from your mouth. This bacterial ecosystem doesn’t get along well with bacteria from the waste and kicks them out. This doesn’t mean there are no waste pathogens on your toothbrush, just that the natural bacteria from the toothbrush reduces their numbers. ⁽⁶⁾

You’d think that closing the toilet lid solves everything. However, fluid dynamics analysis suggests that’s not really the case. It’s been demonstrated that closing the lid did not significantly reduce the contamination of restroom surfaces with viral particles. When the lid is closed, the aerosols can’t escape upwards, but they can escape laterally. They don’ climb has high, but are pushed sideways.

Separation helps. Ensure the toothbrush is at least 2 meters away for the toilet, and if possible, significantly more. Locking it in a cabinet also helps, as long as there’s enough circulation in the cabinet for the toothbrush to dry.

So, what can you do?

Use toilet seat covers to protect yourself.

If the toilet has a lid, wipe it before use with an alcohol wipe and close it before flushing to limit plume exposure.

Wash your hands properly for at least 20 seconds using soap and water.

Carry hand sanitizer or antibacterial wipes to clean your hands afterwards if there isn’t any soap.

Avoid hand dryers, if you can, as they can spread germs. Use paper towels instead.

Sanitize your phone regularly and don’t use it in the toilet.

Clean baby changing areas before and after use, and always wash or sanitize your hands. (4)

Resources

1. Bryn Nelson, Flush, (New York, Grand Central Publishing, 2022)
2. Sarah Kuta, “Here’s what really happens when you flush a toilet,” smithsonianmag.com, December 13, 2022
3. John P. Crimaldi et al., “Commercial toilets emit energetic and rapidly spreading aerosol plumes,” Scientific Reports,12, Article number 20493 (2022)
4. Lotti Tajouri, “The truth about public toilets, according to science,” sciencealert.com, September 28, 2025
5. Richard Gray, “Your toothbrush is bristling with bacteria—is it time to change it, bbc.com, October 19, 2025
6. Mihai Andrei, “Can bacteria from the toilet really travel to our toothbrushes? zmescience.com, January 27, 2026

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