Fog in the airplane? Here's why you shouldn't worry

It might look a little disconcerting, but when humidity causes fog in an aircraft it's nothing to worry about. (Vajirawich Wongpuvarak / iStockphoto)

It’s a phenomenon you might be familiar with if you’ve ever boarded an airplane on a humid day. Hot, muggy air from the outside meets the cool air on the inside that’s blasting from the aircraft air conditioning vents – temporarily creating what looks like mist or fog inside the cabin.

A couple weeks ago, TikTok user Savannah Gowarty posted a video of inflight mist and condensation on a domestic U.S. flight. The video garnered over 13.1 million views, with amazed and confused commentators questioning what was going on.

Short answer: it’s a natural occurrence that usually only lasts a short while, and it’s nothing to worry about.

“On hot and relatively humid days, cold air from the aircraft’s air conditioning system mixes with the warmer, humid cabin air and lowers it to the dew point, creating fog,” a Federal Aviation Administration (FAA) spokesperson tells CNN Travel.

“The fog is generally short-lived as the cooled air quickly warms above the dew point.”

Scientific explanation

When an airplane is waiting on the ground pre-departure, the aircraft cabin air is kept cool “either from an external ground air conditioning unit or the aircraft’s own Auxiliary Power Unit (APU),” as the FAA spokesperson explains.

“Both provide cold air (usually much cooler than the ambient temperature) which can temporarily lower the dew point of the aircraft cabin air enough to create fog.”

Climate scientist Indrani Roy, who works at University College London, says that the environment on board an airplane also creates perfect conditions for condensation in the cabin. That’s why cabin surfaces – and people – might feel damp. Condensation occurs when water vapor in the air - which is “prone to sticking,” as Roy puts it – comes into contact with any cooler solid surfaces, and there are plenty of solid surfaces inside an aircraft.

“Hence condensation is more likely in the cold solid surface areas of the cabin,” Roy says.

Roy also emphasizes that neither mist nor any resulting condensation is “cause for alarm.”

But although humidity-fueled fog is perfectly safe, passengers can sometimes be “concerned,” especially when they experience it for the first time, says U.S.-based flight attendant Rich Henderson.

It’s usually because they’ve mistaken the fog for smoke, Henderson tells CNN Travel.

“But a quick explanation usually helps to ease any nerves that they may have,” says Henderson, adding that, generally speaking, passengers “don’t get too upset very often.”

“Mostly they are just confused about what it is. But once you explain to them it’s just condensation from the cold air of the aircraft’s air conditioning system meeting the warm humid air of the cabin, they understand pretty quickly.”

Passengers usually see the humorous side too, Henderson adds.

“I usually make a joke that it’s just like we’re in an ‘80’s music video and that usually gets people laughing about it pretty quickly.”

Gone in seconds

For flight attendants, judging whether passengers would prefer a slightly longer, scientific explanation or a more humorous shorter take is a part of their skillset they hone on the job. Henderson says such people skills aren’t something that’s particularly really taught in training, but it’s something you quickly pick up on when you’re interacting with different people, with different perspectives, daily.

Anything that’s “unfamiliar to passengers can cause some anxiety from time to time,” says Henderson – pointing to unexplained noises or engine sounds as another culprit.

“A simple explanation and a little joke usually does the trick.”

So there you have it – airplane fog is nothing to worry about, and just a chance for you to embrace your inner ‘80s pop star.

And while you might be concerned about the fog ruining your blow dry, “aircraft cabin fog usually dissipates very quickly,” the FAA spokesperson explains.

“This is due to the colder air (which lowered the cabin air temperature to its dew point) quickly warms back above the dew point. Once that happens, the fog will disappear.

Many times, the fog only appears as it comes out of the vent, exists for 1-2 seconds and then is gone.”