Go to Brilliant.org/SciShow to learn more.

[♩INTRO]

Growing up, you may have heard that you can catch a cold in the rain.

And it turns out there's some truth to that idea.

See, pathogenic organisms

stuff like viruses and bacteria that can give plants and animals diseases

do rain down on us all the time, with or without the help of water.

But the situation isn't so dire that you're likely to get sick from going outside… yet?

According to a 2015 study published in

the Proceedings of the National Academy of Sciences,

we may inhale thousands of microbes per hour when we're breathing in “fresh air”.

These organisms come from almost anything you can think of:

the soil, bodies of water, even the surfaces of plants and buildings.

And they're not necessarily from the immediate vicinity.

Winds, splashing water, rising smoke, and many human activities can dislodge

microorganisms from their dwelling places and launch them into the air.

Once afloat, they can snag onto small particles like dust

and travel way up into the atmosphere,

into a region known as the planetary boundary layer.

And there, they can move thousands of kilometers

with the air masses they're suspended in, across whole continents and oceans.

Eventually, though, they fall back down,

either in rain or when the particles they're associated with finally settle.

And scientists estimate that hundreds of millions of viruses

and tens of millions of bacteria rain down in this manner

on every square meter of this planet every day.

That's... not the worst part.

You see, scientists say these globe-trotting microbes

can spread diseases around the globe.

For example, in 2004, a pathogen that infects plants

traveled from Asia to the United States thanks to a hurricane.

And a 2003 paper published in BioScience suggested that

the global transport of dust could be sprinkling pathogens onto coral reefs.

Poor coral reefs just can't catch a break, can they?

Luckily, if you're a human, you probably don't have too much to worry about.

Most of the microorganisms moving around this way are considered harmless.

...Though, not all of them.

Scientists have found potential pathogens like Staph

in the dust that settles after storms and during dust events.

And in some cases, they think wind patterns can explain disease outbreaks.

For example, in 2011, researchers found that epidemics of Kawasaki disease

correlated with wind currents that swept from Asia to the north Pacific.

Kawasaki disease is an illness that causes inflammation in blood vessels,

particularly in kids.

And the weird thing is, we don't actually know which pathogen is responsible.

So the wind pattern connection, while not definitive, could be an important clue

for medical researchers trying to better understand the disease.

Also... even if there's no immediate link between

human disease-causing pathogens and the billions upon billions of microbes

falling from the sky every day, there could be soon.

See, this whole situation is probably getting worse with climate change.

Scientists think it's likely that even more dust and microbes will float

into our atmosphere in the coming decades

thanks to things like increased desertification and more intense weather events.

So, while you might not catch a cold or any other disease from the rain

in the near future, the possibility is only increasing.

Researchers have to use a lot of really complex math to figure out how

pathogens move around in the clouds and how that might change in the future.

And that math is something everyone can learn with Brilliant.org.

You see, Brilliant offers dozens of courses that cover topics in science,

engineering, computer science, and math.

And their Differential Equations 2 course dives into the hardcore math

needed to predict weather patterns, as well as other kinds of scientific modeling.

With a premium subscription, you'll get access to it and all their other courses,

as well as engaging Daily Challenges

which help you practice the skills you're learning.

And right now, the first two hundred people to sign up at Brilliant.org/SciShow

will get 20% off an annual premium subscription.

So check it out!

And let us know if you learn anything really cool in the comments.

[♩OUTRO]