Rinsing out your mouth

Here’s a thought experiment with an obvious answer. Imagine you are sitting at the end of a row of seats in an airport waiting area. There are ten people to your right. A man at the far end has a glass of water. He takes a big mouthful, swishes it around thoroughly, and spits it back in the glass. He hands it to the person to his left, who takes a big mouthful, swishes, and spits it back in the glass. This person hands it to the next person, who does the same. By the way, all these people are strangers to each other. And so it goes, down the line, until this murky glass of water reaches you. Do you follow their example? 

Of course not. That would be dangerous and disgusting. There is no way you would mix bodily fluids with strangers. 

But you do. Probably every day. Not with liquid water in a glass, but with vapor in the air. 

Most indoor public places in the U.S. have abysmal air quality. That is, poor circulation, minimal air changes, and no filtration or sterilization. When you inhale in an airport, a classroom, an office, or a restaurant, some of the air you take in has been in the mouth, nose, and lungs of multiple strangers. 

When we exhale, the air we exhale contains microscopic aerosol particles that carry bacteria and viruses and can linger in the air for hours. Even aside from these gifts, hand made in the mucous membranes of people you have never met, there are volatile organic chemicals, fungal spores, pollen, and P2.5 particulates (the kind that lodge deep in your lungs). 

Another thing that people exhale is carbon dioxide. Outdoors, the CO2 level is somewhere around 420 parts per million. Indoors, this level can reach 1,500 to 3,000, or more in poorly ventilated, crowded spaces. There has been plenty of research on the effects of high CO2 levels on cognition. Even 1,000 ppm of CO2 can reduce people’s ability to make rational decisions by 25-50%. People’s ability to think drops in direct proportion to rising CO2 levels. This shows up in poorer outcomes for students, workplace accidents, and diminished productivity. In healthcare facilities, poor air quality results in poor decision making, with obvious results, and secondary infections, with more obvious results. 

Around the turn of the 20^th century, there was a revolution in public health. Cities got serious about dealing with sewage and clean water. People realized that it was important to prevent what comes out the bottom of you from going back in the top of you, and did something about it. Child mortality rates plummeted. Just a few years ago, the few schools that implemented air quality measures at the beginning of the Covid pandemic had significant drops in sickness and absenteeism. 

There are devices called heat recovery ventilation systems. They take contaminated indoor air and, without mixing, preheat or pre-cool incoming fresh air. This saves most of the energy that would be lost to direct ventilation. This kind of air handling is also an opportunity for fine filtration. There are better versions of standard furnace filters that will catch small particles, including the aerosol particles that carry viruses. There are ultraviolet (UV) lights that can be installed in ducting that kill microbes as they float past. There are far-UV lights that can be used directly in a space to lower the microbial burden in the air. 

Then there is the Corsi-Rosenthal box, the simplest, fastest, and cheapest way to clean air, if not lower CO2. It’s made of four 20”x 20” MERV 13 rated furnace filters and a standard 20” box fan, plus a roll of duct tape. There are directions online. You end up with a 24” cube that will plug into the wall and clean the air for about $50. Some companies such as cleanairkits.com are refining the C-R box with nearly silent gamer computer fans. You can have a suitcase sized filter that will cycle the air in a reasonably sized room every five minutes, and you will barely hear it. 

Today, we are still treating indoor air the way we treated water 200 years ago. We have an incredible opportunity to improve our health, the learning abilities of our children, and our own comfort and productivity at work. It’s not really complicated, and considering the economic losses we suffer today from polluted indoor air, it is comparatively cheap. And then there’s the reduction in suffering. Imagine not getting colds or the flu every winter. Not getting long Covid, or any of the diseases that follow Covid. Think about reducing your chances of getting all the other diseases that result from contaminated air. It’s the most obvious and effective public health measure we could implement as individuals, municipalities, institutions, states, and as a nation. 

But of course, like contaminated air, the problem is invisible. People don’t burst into flame when they breathe polluted air. The effects are slow and silent, seemingly random, and apparently disconnected from the cause. The countermeasures have been made into political symbols. Everyone is willing to save pennies today to spend dollars next year. 

This is something you personally can change. Invest some small amount for a Corsi Rosenthal box or its ready made equivalent for your personal and/or work space. Be an advocate for clean air in the local schools. Clean, low CO2 air would cause a stair step jump in test scores. 

Point out to your employer that they are throwing money away by having their employees suffer from dirty air and high CO2. An average office building costs $2-$4 per square foot annually for utilities. Businesses are always trying to bring this cost down. On the other hand, the cost of the employees that work in that space could be expressed as hundreds of dollars per square foot. Improving the productivity and cognitive ability of those employees by even 5% would wipe out the cost of heating, cooling, and lighting. Basic improvements in air quality can do much better than 5%. 

Clean indoor air is, I was about to say “a no-brainer,” but it is about preserving your brain, along with the rest of your body. Or, may I interest you in a slightly murky glass of water? 

https://www.epa.gov/iaq-schools/evidence-scientific-literature-about-improved-academic-performance

 https://www.nsba.org/resources/asbj/asbj-april-2025/april-2025-students-learn-better-with-clean-air

 https://hsph.harvard.edu/news/office-air-quality-may-affect-employees-cognition-productivity/