Toilet water spray, technically called a “toilet plume,” can shoot upward at speeds reaching 5 meters per second and rise more than a meter above the floor within seconds of a flush. The droplets are mostly invisible to the naked eye, with the vast majority smaller than a human hair’s width, and they carry bacteria and viruses from the bowl into the surrounding air and onto nearby surfaces. The actual reach of the plume depends on toilet type, flush pressure, ventilation, and whether the lid is down, and some of the answers from recent research are not what you would expect.
What the Plume Actually Looks Like
You cannot see it happening, but researchers have made the plume visible using laser illumination. A 2022 study at the University of Colorado used lasers to track aerosol particles shooting out of a commercial flushometer-type toilet in real time, capturing the speed and spread of the ejected cloud.1PubMed Central. Commercial toilets emit energetic and rapidly spreading aerosol plumes What that study and others have revealed is that the plume is made up of an enormous number of tiny droplets. A single flush of a squat-style toilet, for example, can produce roughly 590,000 droplets, though more than half of those fall back into the water and the rest rapidly shrink into even tinier particles called droplet nuclei within about five seconds.2PubMed. Induced two-phase air-water flows and droplet emissions after flushing a squat toilet
The droplets themselves are overwhelmingly microscopic. Measurements across multiple toilet types consistently show that about 95 percent of the droplets are smaller than 2 micrometers in diameter, and over 99 percent are smaller than 5 micrometers.3PubMed Central. Aerosol Generation by Modern Flush Toilets A separate study found that 92 percent of flush-generated droplets were smaller than 1 micrometer.4PubMed. Study on the air gap effect when closing toilet lid on droplet and pathogen escaping from flushing That size matters because particles this small behave more like gas than liquid. They float, drift with air currents, and can stay suspended for a long time rather than falling to the ground quickly.
How High and How Far the Spray Reaches
The upward reach of the plume depends heavily on how much energy the flush puts into the water. An aircraft toilet, which uses a powerful vacuum-assisted flush, generates a plume with an upward velocity of about 5 meters per second, and the rising column of droplets reaches more than one meter above the floor.5Building and Environment. Measuring the flushing-generated flow and aerosols in lavatory of commercial aircraft That aircraft study also found that background particle counts in the bowl area roughly quadrupled after flushing, jumping from about 400 particles per liter to around 1,550 particles per liter at peak, before dropping back to pre-flush levels.
Commercial flushometer toilets, the kind you find in office buildings and airports, tend to produce especially energetic plumes because they use high-pressure water delivered from the supply line rather than gravity from a tank. Research comparing flush mechanisms found that the high-pressure flushometer produced statistically greater aerosol emissions than lower-pressure systems. Gravity-fed cistern tanks, the standard in most homes, generated fewer airborne particles, and varying the height of the tank did not make much difference.6Oxford Academic. The potential spread of infection caused by aerosol contamination of surfaces after flushing a domestic toilet So if you have noticed public restroom toilets seem to flush with startling force compared to your toilet at home, you are right, and that force translates directly into a bigger, faster aerosol plume.
The horizontal spread is harder to pin down with a single number, because once the tiny droplets become airborne, they travel wherever air currents take them. In a hospital-based study, researchers measured bioaerosol concentrations at different distances from the toilet after flushing and found that concentrations were not significantly different across distance from the toilet.7PubMed Central. Bioaerosol concentrations generated from toilet flushing in a hospital-based patient care setting In practical terms, this means the aerosol is not just hovering above the bowl. It disperses throughout the bathroom.
What Is Actually in the Spray
The plume would be mostly a curiosity if it were just water vapor. The concern is that it carries whatever is in the toilet bowl into the air, and that includes microorganisms. When researchers seeded toilet bowls with known pathogens and then flushed, the results were consistently alarming.
In experiments with Clostridium difficile, a bacterium that causes severe diarrhea and is a major problem in hospitals, researchers found that a single flush launched an average of 36 colony-forming units into the air immediately. The majority of those were recovered within the first five minutes, but detectable amounts lingered for over an hour: 8 colony-forming units at 60 minutes and 3 at 90 minutes after a single flush.8Journal of Hospital Infection. Potential for aerosolization of Clostridium difficile after flushing toilets: the role of toilet lids in reducing environmental contamination risk A more recent risk assessment confirmed that a single flush can produce C. difficile bioaerosol concentrations of roughly 30 colony-forming units per cubic meter of air, and deposit about 8 to 11 colony-forming units on nearby surfaces.9PubMed. Evaluating the risk of Clostridioides difficile infection from toilet flushing: a quantitative microbial risk assessment and implications for infection control
Viruses are also carried in the plume. A study testing for multiple viruses in a healthcare setting found viral contamination on 78 percent of surfaces and in 81 percent of air samples collected in restrooms, with human adenovirus strains sometimes matching across the toilet water, surface swabs, and air samples simultaneously.10PubMed Central. Viral contamination of aerosol and surfaces through toilet use in health care and other settings Norovirus, the most common cause of gastroenteritis outbreaks, has also been detected in flush-generated aerosols. Researchers using murine norovirus as a stand-in for the human version measured concentrations of 383 to 684 viral RNA copies per cubic meter of air after flushing.11PubMed Central. Determination of murine norovirus aerosol concentration during toilet flushing Norovirus is known for having an extremely low infectious dose, which makes even small amounts aerosolized from a toilet bowl potentially meaningful.12PubMed Central. Aerosol Transmission of Norovirus
The Contamination Does Not End After One Flush
One finding that surprises people is how persistent the contamination can be. Flushing does not fully clear pathogens from the bowl. In an experiment with C. difficile spores, researchers found that spores remained detectable in the bowl water even after 24 consecutive flushes. Each subsequent flush continued to launch some spores into the air, though the numbers declined over time. Large-droplet contamination on nearby surfaces accumulated over the entire 24-flush sequence, meaning each flush added to the deposit left by the previous ones.13PubMed. Toilet plume aerosol generation rate and environmental contamination following bowl water inoculation with Clostridium difficile spores
A similar pattern was documented with bacteria like Serratia and with bacteriophage MS2, a virus commonly used as a lab proxy. The highest airborne counts occurred after the first flush, but sequential flushes continued to distribute organisms into the air at progressively lower levels. Organisms clinging to the sidewalls of the bowl, not just those floating in the water, contributed to the aerosol.6Oxford Academic. The potential spread of infection caused by aerosol contamination of surfaces after flushing a domestic toilet The practical takeaway: if someone in your household has a stomach bug, the toilet bowl remains a reservoir of their pathogens for many flushes afterward.
Does Closing the Lid Actually Help
The standard advice is to close the toilet lid before flushing. Intuitively, this should work as a physical barrier. And some research supports it: the C. difficile aerosolization study found 12-fold greater bacterial counts in the air at seat level when the lid was open compared to when it was closed.8Journal of Hospital Infection. Potential for aerosolization of Clostridium difficile after flushing toilets: the role of toilet lids in reducing environmental contamination risk A computational simulation of a public washroom found that closing the lid reduced aerosol exposure for people standing farther away by about 90 percent.14Aerosol and Air Quality Research. The Dispersion and Exposure to Aerosols From Toilet and Urinal Flushing Under the Effect of Closing Toilet Lid and Different Ventilation Rates in a Public Washroom
But there is a catch. That same simulation found that while closing the lid reduced exposure for people standing at a distance, it actually increased the exposure of the person standing right next to the toilet. The lid traps the plume temporarily, but when the person lifts it afterward or when aerosols leak through the gaps between lid and bowl, the person closest to the toilet gets a concentrated dose.
Even more striking, a 2024 study testing actual virus contamination on bathroom surfaces after flushing found that viral contamination of restroom surfaces did not depend on whether the lid was up or down.15PubMed. Impacts of lid closure during toilet flushing and of toilet bowl cleaning on viral contamination of surfaces in United States restrooms The toilet seat bottoms accumulated enormous viral loads regardless of lid position. The aerosol escapes through the gaps around the lid, and the surfaces closest to the bowl get contaminated either way. Closing the lid is not useless, but the evidence suggests it is far less protective than most people assume, especially for the surfaces you actually touch.
It is worth noting that many public restrooms, particularly in the U.S., have toilets with no lids at all, making the point moot for a large percentage of real-world toilet encounters. A survey of hygiene behaviors in Hong Kong found that about 44 percent of respondents reported never closing the lid before flushing.16PubMed Central. A mixed-methods study on toilet hygiene practices among Chinese in Hong Kong
Toilet Type and Flush Pressure Make a Bigger Difference
Not all toilets produce the same plume. The type of flush mechanism is one of the strongest predictors of how much aerosol a flush generates. Research directly comparing high-pressure flushometers to gravity-fed cistern tank systems found that high-pressure systems produced significantly more airborne pathogens. The cistern tank system, the kind most residential toilets use, generated fewer emissions across all tested microorganisms. Interestingly, changing the height of the cistern tank did not meaningfully change the amount of aerosol produced, suggesting that flush volume matters less than flush pressure.
Aircraft toilets represent an extreme case. Their vacuum-assisted flush creates a plume with the highest measured velocities in the literature, and that plume pushes roughly 8,500 aerosol particles larger than 0.3 micrometers into the small cabin lavatory per flush, 92 percent of which are submicron.5Building and Environment. Measuring the flushing-generated flow and aerosols in lavatory of commercial aircraft The tiny size of an airplane lavatory amplifies the problem, as there is nowhere for the aerosol to go except the surfaces immediately around you and the air you are breathing.
Ventilation, Cleaning, and What Actually Reduces the Risk
If closing the lid offers less protection than expected, what else works? Ventilation turns out to be one of the most effective defenses. Simulations of bathroom ventilation found that increasing the air exchange rate from 10 to 40 air changes per hour improved the efficiency of aerosol removal by 236 percent, and redesigning the exhaust placement could more than double that improvement further.17Journal of Hazardous Materials. Ventilation reconstruction in bathrooms for restraining hazardous plume: Mitigate COVID-19 and beyond A separate study confirmed that a higher air change rate and a louvered bathroom door both improved exhaust ventilation performance for removing bioaerosol particles after flushing.18Building Services Engineering Research and Technology. Exhaust ventilation performance in residential washrooms for bioaerosol particle removal after water closet flushing For your home, running the exhaust fan during and after flushing makes a real difference, especially if someone in the household is sick.
Chemical cleaning also helps, though the timing matters. Testing hospital-grade disinfectants on surfaces contaminated by toilet flushing showed that all disinfectants significantly reduced viral concentrations when they were given at least 15 minutes of contact time. Peracetic acid and quaternary ammonium compounds were the most effective at reducing virus in the toilet bowl itself, while hydrogen peroxide performed poorly against organic-matter-laden toilet water.19PubMed. Evaluation of hospital-grade disinfectants on viral deposition on surfaces after toilet flushing Automatic toilet bowl cleaners that release surfactant with each flush have also been shown to significantly reduce the number of bacteria ejected into the air, with more surfactant producing better results.20Applied Microbiology. Reduction of microbial aerosols by automatic toilet bowl cleaners The surfactant likely works by reducing the surface tension of the water, which suppresses the bursting of bubbles that generates the aerosol in the first place.
How Much Aerosol Lingers After Flushing
The hospital-based study that measured bioaerosol at different distances from the toilet also looked at how concentrations changed over time. Bioaerosol levels were not significantly different across sampling times, meaning that the aerosol generated by a flush could still be measured more than 30 minutes later at comparable levels.7PubMed Central. Bioaerosol concentrations generated from toilet flushing in a hospital-based patient care setting This makes sense given the particle sizes involved. Particles under a few micrometers settle extremely slowly under gravity and can remain suspended in still indoor air for hours. In a poorly ventilated bathroom with no exhaust fan running, the aerosol from a flush is still hanging in the air when the next person walks in.
This persistence has implications for shared bathrooms in homes, hospitals, and public spaces. If you enter a restroom stall shortly after someone else flushed, you are breathing air that likely still contains aerosol from their flush, regardless of whether they closed the lid.
Does Toilet Plume Actually Make People Sick
Given all the evidence that toilets launch pathogens into the air and onto surfaces, you might assume there would be documented outbreaks traced back to toilet flushing. But a comprehensive literature review on the topic concluded that no studies have yet clearly demonstrated or refuted toilet plume-related disease transmission, and that the significance of the risk remains largely uncharacterized.21PubMed Central. Lifting the lid on toilet plume aerosol: A literature review with suggestions for future research
This is not the same as saying the risk is zero. Proving that a specific infection came from a toilet flush rather than from touching a contaminated door handle, or from direct person-to-person contact, is extremely difficult. Epidemiological studies would need to control for all other exposure routes, which is nearly impossible in real-world settings. The lab evidence that pathogens aerosolize during flushing is strong and consistent. What remains uncertain is how often the doses people actually inhale or pick up from surfaces reach the threshold needed to cause infection. For a hardy pathogen like C. difficile, which forms resilient spores, or norovirus, which can cause illness from a tiny dose, the theoretical risk is higher than for organisms that require larger infectious doses or do not survive well in aerosol form.
Your Toothbrush and Other Bathroom Items
The fact that toilet aerosol disperses throughout the bathroom raises an obvious concern about items stored near the toilet, with toothbrushes being the example that alarms people the most. Given the evidence that bioaerosol concentrations do not drop off much with distance from the toilet and can persist for over 30 minutes, anything stored openly in a bathroom with a toilet is exposed to whatever the plume carries. This does not mean your toothbrush is a major infection risk on any given day, but during periods when a household member has a gastrointestinal illness, the exposure becomes more meaningful.
Practical steps are fairly simple: store toothbrushes in a closed cabinet or a different room if possible, use the exhaust fan every time you flush, keep a surfactant-based bowl cleaner in the toilet if someone in the household is sick, and clean high-touch surfaces around the toilet regularly with a disinfectant that gets adequate contact time. Closing the lid before flushing still makes sense as one layer of defense, even if it is less effective than once thought, because it does reduce the initial burst of larger droplets even if fine aerosols escape through the gaps.