It's easy to look at the white trail behind a jet aircraft and imagine all manner of chemicals raining down from above.

Could they be harmful?

Could it be some sort of conspiracy?

The truth is out there -- in the form of some pretty straightforward chemistry.

Chemtrails are made of mostly water, because that's what happens when the chemistry of burning jet fuel meets the chemistry of air.

Here's how that works.

Jet fuel is mostly made of stuff like these molecules here.

These are hydrocarbons, which are chains or rings of carbon atoms with hydrogens hanging off the sides, and there are a whole bunch of different kinds in jet fuel.

The chemical bonds holding those molecules together are a source of energy which gets released by burning and, when thrown out the back of the engine, propels the jet plane through the sky.

But the carbon and hydrogen have to go somewhere when the bonds are broken.

They mix with oxygen, creating carbon dioxide and water.

There's a little bit of extra stuff in there too, like nitrogen and sulfur, which reacts to form sulfur dioxide.

The products are expelled from the jet engine and trail along behind the plane.

But water is clear.

So why's it leaving a visible trail?

What's going on in a jet engine are basically the same chemical reactions as in the engine of a gasoline-fueled car.

On cold days you can see the exhaust coming out of the tailpipe -- that's mostly water.

The same thing happens with the water leaving the jet, except much more extreme.

At a commercial plane's cruising altitude of 35,000 feet, the temperature is around minus 50 C. Minus 50 isn't unheard of in Antarctica, but that's pretty flipping cold.

Depending on the exact conditions the water can freeze into ice crystals, or condense into liquid droplets.

The sulfur impurities really help get the droplets going.

But whether it's water or ice, those puffy white trails are made up of bits of H2O scattering light so we can see it.

Which means they aren't CHEMtrails, except in the sense that water is a chemical.

They're more technically known as CONtrails, short for condensation trails.

The scientific community is pretty well agreed on the subject of chemtrails being contrails.

One study surveyed experts in the field of atmospheric chemistry and asked them whether they had, in their entire career, ever seen evidence for a secret large-scale atmospheric spraying program, or SLAP for short.

99% of the experts surveyed said no, which is way more consensus than the 4 out of 5 dentists telling you to chew a given brand of gum.

So unless they're crop dusting or cloud-seeding, all those jets are leaving behind is their own watery exhaust.

Thanks for watching.