Compiled by Lydia Goode
Handling a hygiene crisis
Picture yourself waiting to be served at a bar, when you notice the staff have kindly laid out several bowls of welcome morsels. Think Goldfish Crackers, or Cheddar Bunnies. Before you grab a few, here’s something else to think about. How many have sampled before you? Had they just exited the restroom? Did they wash their hands?
Such concerns could have been the motivation behind what is arguably America’s most organized episode of bathroom stalking. This is described in a 2013 study published in the Journal of Environmental Health. Twelve brave researchers were recruited to unobtrusively record hand-washing routines in a college town’s restrooms. As unlikely as it might seem for an investigator to successfully pose as an innocuous bystander in a public toilet, when he/she is equipped with a paper pad and a Sharpie, plus a fascination with soap and faucets, a surprising 3,749 individuals failed to notice their hand hygiene was under review. Men (what a surprise!) were the least fastidious; 15% of them made no effort to clean up, and 35% of them wet their hands without using soap (the corresponding data for women? 7% and 15%, respectively – way to go, girls!).
However, among those individuals who did wash their hands, a paltry 5% adhered to CDC guidelines: 20 seconds of scrubbing with soap as well as water. Bottom line: almost nobody does this properly.
You might be tempted to think that personal hygiene has improved over the years, particularly post-Covid. So, let’s test this assumption with a callout to America’s “leading manufacturer of commercial plumbing fixtures and washroom accessories”: Bradley Corp. Since 2009, this company has posted results from its annual Healthy Handwashing Survey. Over 1,000 American adults were quizzed in 2025. Almost a quarter of the men confessed to not washing their hands after a bathroom visit; half of them did not use soap.
No more bar snacks for me.
Playing laser tag with toilet plumes: it's a blast
From time-to-time, needs must: you have to resort to a public restroom.
You are right to be concerned. Toilet bowls harbor persistent pathogens: reported examples are the SARS coronavirus, and species of Staphylococcus and Legionella. These disease agents are poised for the next flush, whereupon they will launch their airborne assault within an invisible plume of aerosol particles. The risk is elevated in healthcare settings.
So, you might take solace from this being a topic for academic study. There are scientists who aim to reduce this infection risk by testing the value to plume reduction of novel flush valve cycles, bowl geometries, and disinfection strategies. To accomplish this, they are improving the methods used to quantify particle paths and flight times of toilet plumes.
In 2021, one such research team at the University Colorado Boulder described their new experimental design in the journal Scientific Reports. Here, Professor John Crimaldi and his colleagues, from within the Department of Environmental and Architectural Engineering, described their laboratory setup in which a pulsed laser is fired at a flushing toilet. The particles within the blast of aerosol disrupted the path of the laser, causing light scatter, which was itself monitored by high resolution cameras.
The human eye’s version of the resulting green plume – up to five feet high – is depicted both in in their paper and arguably more dramatically via Professor Crimaldi’s article in The Conversation. In that online post, Prof. Crimaldi explains that their new method illuminates the aerosol spread, but more accurately and quantitatively than prior methods, which involved the placement of air samplers, or computational models.
Professor Crimaldi’s team notes that as bad as their plumes seem, they are likely diluted by their well-ventilated laboratory, which lacked partitions. More concentrated plumes can be expected in real-life. The scientists also acknowledge they did not test the influence of either toilet paper or fecal matter (good luck adding poop to the experimental protocol!).
These authors further propose the target range of plumes could be reduced by closing the lid. Professor Charles Gerba would disagree. A study published by his group at The University of Arizona found no impact of lid closing upon contamination spread. The American toilet lid is raised half an inch above the bowl, a standing invitation for plumes of toilet waste to eject out of the gaps.
Consequently, after I have finished visiting the facilities, I utilize the positive pressure of my airways to reduce the chance of infection; I exhale while flushing. Then I exit the area like it’s an emergency situation. “But wait”, I hear you ask. “Without washing your hands?” Well, would you want to linger in the plume for 20 seconds?