What It Really Means When You See Fog Randomly Appear In The Aisles Of A Plane

You've just sat down in your assigned seat and are settling in for a long flight when you notice something peculiar in the airplane: A strange white fog is billowing around the ceiling above the aisle. Seeing anything unexpected on your flight can feel like a nightmare, but in general, it's perfectly normal to see a little of this white mist blowing around the cabin — and doesn't indicate that anything has gone wrong.

Obviously, that doesn't mean that you should ignore signs of smoke during your flight. Fires can occur on planes, and smoke filling up the cabin is a serious concern. Electrical fires, in particular, tend to produce a large amount of thick, white smoke that can be very dangerous, but due to the smell and how irritating it is to the eyes, it's unlikely that you would mistake smoke for fog. If you're unsure, feel free to ask a flight attendant if everything looks normal — but in general, seeing white fog on a plane is no reason to be nervous.

It's hot and humid outside

In 2019, CBS New York reported a massive amount of thick, white fog had filled a plane that was taking off from balmy Florida. In this case, there was so much dense, white fog that it was impossible to see in the airplane. That amount of fog is extremely unusual, but this bizarre event and the typical wisps of mist in the air have the same cause: humidity and temperature.

While it might seem bizarre to see fog in an airplane, it's actually happening for the same reason that we usually see fog over lakes and rivers — warm conditions meeting cool conditions. During takeoff, outside air comes into the cabin through the vents above the overhead luggage bins. If the weather outside is hot and humid compared to the air inside the airplane (which it often is, since airplanes are typically cool and dry) clouds can form. This can also happen as the air conditioning is first turned on. Typically, these things happen at the beginning of a flight, so if you're noticing fog during takeoff, this is very likely the cause.

It could be intentional

Usually, the fog that occurs on flights is naturally occurring, but in some cases, a similar-looking mist may be intentionally pumped into your flight. As unsettling as it might be to see an unfamiliar substance floating around the overhead bins, sometimes it's an intentional choice by the airline to make you more safe and comfortable. 

For one thing, the inside of a flight is dry — drier than almost anywhere else you're ever likely to be. This can be unpleasant and uncomfortable for passengers and cabin crew alike, leading savvy passengers to pack Vaseline and extra water bottles on flights. Some airplanes include humidifier systems to help out passengers, especially those in first class. In some situations, this could potentially cause a little fog, but it certainly makes it more pleasant for those onboard.

A fog could also be due to crew members disinfecting the plane. Some spots on airplanes are notoriously dirty, but since the global pandemic, airlines have started spraying disinfectant in the form of a mist to kill germs on plane surfaces. Usually, this cleaning is performed before and after flights when nobody is onboard, but sometimes, the crew may disinfect during very long flights to keep the cabin from smelling too sweaty or musty.