And now a few years removed from a pandemic lockdown, and it's still kind of weird to think about.

Viruses and bacteria are these invisible enemies that we just kind of deal with day to day, and they leave us coughing and sneezing our way through winters.

So we wield our sprays and wipes and sanitizers.

But there is a powerful disinfectant that we've known about for a century and it still isn't part of this tool kit.

At least not consistently.

Light.

This is the electromagnetic spectrum.

You've seen it before, literally here where visible light is.

The light we're talking about as a disinfectant occurs here: Ultraviolet light.

There are actually three different types of UV light that occur at different wavelengths.

The one shining down on us from the sun is mostly UVA and some UVB.

And that UV does all the things that people think UV is going to do so we can't shine it on people. Ok?

It hurts your skin, it hurts your eyes, it gives you cancer.

It does that by damaging the DNA in our cells, but ironically, those same properties that cause cancer also break down viruses and bacteria and stop them from replicating.

And we've known this since the late 1800s.

So researchers have been experimenting with low wavelength UV or UVC as a germicide for decades.

In the 1940s, researchers placed UV irradiation chambers in classrooms.

Now, don't worry, the UV light was being safely projected into the air above the children so they weren't being directly exposed to it.

But as air circulated the room, it could be cleansed.

Researchers ultimately found that it was effective at stopping the measles virus.

Very effective.

Under 15% of the kids in classrooms with UV were infected, compared to over 55% of those in classrooms without it.

Later studies used rodents to test UVS effectiveness with other diseases like tuberculosis.

The air was irradiated with ultraviolet light first and the hamsters in the treatment group did not get tuberculosis.

But these lights needed to be kept above people or hamsters and installed carefully using a costly process called upper room UV.

Because even though they operate at a low wavelength, it still isn't great to directly blast humans with it day in and day out. You know, because the cancer thing.

This method is actually used in a lot of hospitals, paired with ventilation to help reduce infection rates.

But having UV at the top part of the room can't do much to stop the germs being spread between people.

So more recently, researchers began looking for a better way to kill pathogens all around us.

They ran studies to determine the most UV light that could be used to kill bacteria and viruses but also minimize harm to humans, which brings us to a type of UVC called Far UV.

Far UV has a very low wavelength that can't penetrate skin deeply enough to cause damage, even in mice, specifically bred to be susceptible to cancer.

This is a field full of tuberculosis hamsters and cancer mice, and I feel really bad about it.

In test chambers, Far-UV is really effective at killing pathogens.

This study is from 2020 when, well, you know what happened in 2020.

It showed that Far-UV was able to kill 99% of Coronavirus in a test chamber.

And this study found that it was 98% effective at reducing the bacteria that causes staph infections.

So why isn't it everywhere?

In order to understand effectiveness, you first have to understand safety.

While it's generally accepted that Far-UV won't give you cancer, there are other consequences to bring a UV light so close to the ground.

We know really well that when you shine UV light on air, it can cause chemistry to happen.

UV light produces a molecule called ozone, which can be harmful for humans to breathe in.

If you're exposed to lots of ozone, if you're exposed to lots of particles that your, sort of, risk for respiratory ailments goes up.

But just how much of it is being produced by these lights in a real world environment is still up in the air.

So in what ways can we use it?

That's a UV light behind you.

Yes, it is. Yeah.

So this is a Far-UV light predominantly putting out 222 nanometer wavelength light, which is shown to be very effective in eradicating everything from viruses to bacteria to mold, allergens, and more.

PJ Piper is the CEO of a company called Far UV Technologies that develops all types of UV devices.

He believes that far UV will become more widely used in tandem with other layers of protection.

I don't really look at this as displacing HVAC or filtration.

Those are important things.

They just do different things.

HVAC is predominantly for climate control.

It also has a slight benefit of potentially removing the viral load.

Filtration, similarly, doesn't change the climate control, but it's really important for getting rid of inorganic pollutants like smog or wildfire smoke or something like that.

But there's nothing anywhere near as efficient as light as a source to eradicate the pathogens that might be in the room.

So pairing UV with other systems could help reduce pollutants too.

But Barbara and other researchers suggest we think about the cost-benefit.

I think we could run into trouble. Is if people want to install these lights as a replacement for ventilation?

A hospital where the risk of infection is very high, it could probably benefit from this, but an old school building on an average day, probably less so.

It might be some time before we start seeing Far-UV everywhere.

The odds of a of a next pandemic, it seems to me that it's more a question of when rather than if, and so having technologies like this, I think is super important.

I just want to be careful that we don't get so excited about this kind of technology that we wind up missing something.

Look, anyone trying to sell you a single miracle cure for anything is likely bending the truth.

When it comes to fighting disease, whether that be the common cold or a full pandemic, there's no singular approach.

We need a toolbox of options from vaccines to mask to chemical disinfectants.

And in time, it's likely that Far-UV could be one more addition.

Maybe in various forms that we could bring with us to public spaces or installed somewhere above us without us even knowing as an extra invisible layer of protection against those invisible enemies in the air.

So if you want more info on UV light and germs, you can check out Unexplainable, Vox's Science podcast about unanswered questions.

They're working on an episode that goes deeper into everything we don't know about UV light and disease.

And they'll take you through that original experiment where researchers just decided that kids were better guinea pigs than actual guinea pigs.

It'll come out next Wednesday, February 20th.

But in the meantime, here's a quick preview.

In 1937, 2 researchers had a kind of dangerous idea.

So they figured the perfect place to test it out was in an elementary school on kids on the eve of a massive epidemic.