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The white trails you see in the sky following behind airplanes are made of naturally occurring water vapor. But why and when do planes leave vapor trails?

Planes leave vapor trails in their wake due to condensation forming when the hot exhaust particles meet the humid cool air at high altitudes. As water vapor forms in the air behind the plane, the cold temperatures of high altitude freeze the droplets and they remain in the sky as long white clouds.

Vapor trails are easily one of the most misunderstood aspects of aviation by the general public. What are they? What creates them? Why don’t all planes leave vapor trails? Are vapor trails dangerous? When do planes leave them? As you read through this article, you’ll learn the answers to all of those questions and more. So next time someone asks what those white trails behind an airplane are, you’ll have the answer!

Everything you read below is a combination of our expertise and knowledge, input from aviation experts across various aspects of the industry, and personal research into vapor trails. Everything has been vetted for information to ensure that you’re getting the best, most helpful content that you’ll find anywhere on the web. We hope you enjoy this article and we’re sure you’ll leave knowing everything you need (and want!) to know about vapor trails.

Table of contents


What Are Vapor Trails And Why Do Planes Create Them?

If you look up into the sky throughout the day, chances are high that at some point you’ll see a long and narrow white cloud streaking across the sky. Those certainly aren’t natural clouds that just happened to form in that shape, right? Of course not! These long, white clouds are left in the sky by some airplanes. Oftentimes, you’ll even see a little speck in the air at the front of the cloud, leading the way. That’s right, that’s the airplane way up there.

So what exactly are these white clouds and why do planes leave them in their wake?

Contrary to what many people believe — especially those who are a little into conspiracies — these are not trails of chemicals being released overhead. They have a much simpler explanation; they’re caused by condensation. These condensation trails, or contrails for short, are caused by the normal engine exhaust processes and the surrounding air.

When an airplane is flying, the engines generate and exhaust a decent amount of water out the back in the form of water vapor. When this hot saturated water vapor from the plane’s engine(s) comes into contact with the cool air at high altitudes, it condenses on other particles being exhausted and freezes around them.

Some planes will leave vapor trails that are different from what another plane might leave behind, depending on the aircraft and, more importantly, the air conditions that the plane is flying through. Depending on how moist the air is and the temperature of the surrounding air, the contrails can last for just a few minutes before dissipating.

Or they could last for quite a while longer; a general rule of thumb is that the more humid the air is, the longer the vapor trails are going to last. To add even more variance, the longer-lasting contrails can either spread out as they begin to disappear or they can stay thin and narrow until they slowly just dissipate away.

Why Don’t All Airplanes Leave Vapor Trails?

As you know by now, the vapor trails are simply caused by the combination of engine exhaust, condensation, humidity, and cold temperatures. It doesn’t really have anything to do with the type of plane or anything like that. The fact is, all airplanes don’t leave vapor trails simply because it’s dependent on the conditions of the air around the plane.

To leave vapor trails in the airplane’s wake, the surrounding air needs to be humid enough and cold enough. This is because if the air is not moist enough, then no condensation will form on the engine’s exhaust particles. And if the air is not cold enough (i.e. the plane is not high enough), then the water vapor particles will not freeze and form the “clouds”.

So other than the different engine types between, say, a commercial jet and a small single-engine aircraft, the condition of the air is really the main reason that all planes don’t leave vapor trails. A personal single-engine aircraft typically won’t leave vapor trails simply because it’s not high enough in the air for the air to be humid enough and cold enough to form the small particles of frozen water vapor.

Are Vapor Trails And “Chemtrails” The Same Thing?

This is a bit of an odd question due to the very nature of it, but we’ll do our best to dispel any doubts about vapor trails and what we’re talking about. But we’ll start by answering the question at hand. Yes, vapor trails and “chemtrails” are the same thing. For anyone reading that hasn’t heard of chemtrails before, though, this then of course begs another question.

What are chemtrails?

“Chemtrails” is the shorthand way of saying chemical trails, which is what some people choose to refer to as the white clouds (the vapor trails) left behind by aircraft. Believers in chemtrails think that those clouds are actually a combination of chemicals that are being released high overhead by the aircraft, with a number of different motives.

Those who believe in chemtrails theorize that the chemicals are used to affect the weather, sterilize the population, or even more outlandish things. But let’s be clear in case you are starting to believe some of these same theories. The white clouds left behind by aircraft are not chemicals being dumped into the atmosphere. As described above, they are just naturally occurring trails of condensation.

So long story short, yes, the vapor trails and “chemtrails” do refer to the same thing. But the fact is that chemtrails don’t actually exist and the vapor trails are very real.

Are Vapor Trails Dangerous?

With all those theories about chemtrails that we just briefly mentioned above, your mind might be racing with some ideas of how harmful they potentially sound. And trust me, we’re with you. If those theories on chemtrails were real and they were really dumping chemicals into the atmosphere for any of the reasons above, then we’d be worried too! But what about vapor trails, are they dangerous at all?

This one is much easier to answer: absolutely not! Vapor trails left behind by aircraft are completely harmless. Since they are just caused by condensation and the subsequent freezing of these tiny water particles in the cold temperatures of high altitude, contrails are not dangerous in any way.

Over time, the particles will naturally unfreeze and evaporate in the air. The trails will just naturally dissipate and go away. And you and I will be no worse for wear; they have no effect on us! The environment is also not affected in any way by the vapor trails. At least not any more so than typical airplane engine exhaust affects it. So have no fear when you see white clouds behind airplanes overhead, those vapor trails are totally harmless!

What Else Could Cause White Smoke Behind An Airplane?

Other than the naturally occurring vapor trails that planes leave in their wake, you really don’t want to see any white smoke being left behind an airplane as it flies across the sky. If a plane is leaving white clouds in its wake that aren’t vapor trails, that will typically signify an issue with the aircraft.

Because if it isn’t water vapor — and you know now that it won’t be chemtrails either — then the only other white smoke behind an aircraft would be exactly that: smoke. And if there’s white smoke behind an airplane, that usually means some sort of engine failure. Often, this white smoke will turn black once the failure becomes catastrophic and fires begin. But nonetheless, white smoke typically precedes total engine failure.

But way more often than not, the white clouds behind an airplane will just be harmless vapor trails. So no need to worry if you are flying commercially and look out the window and see white trails being left in the plane’s wake!