What causes fog to form inside airplanes?

Hot and humid air from outside meets cold air inside blown out from the air conditioning vents, resulting in fog inside the cabin temporarily. This phenomenon was captured in a video posted by TikTok user Savannah Gowarty, which garnered over 13.1 million views on a US domestic flight. Many viewers expressed surprise and confusion at what they were seeing. However, experts reassure that this occurrence is natural and nothing to worry about.

The US Federal Aviation Administration (FAA) explained that on hot and humid days, the cold air from the aircraft’s air conditioning system mixes with the warmer, more humid cabin air, causing the temperature to drop below the dew point and create fog. This usually happens when the plane is waiting for takeoff on the ground, as the air in the cabin is kept cool by external air conditioning systems or the plane’s auxiliary engine.

Climate scientist Indrani Roy from the University of London explained that the conditions inside an airplane are conducive to condensation, which is why the cabin surfaces may appear wet. Condensation occurs when water vapor in the air comes into contact with cooler hard surfaces, which are abundant inside an aircraft. While fog in the cabin may make passengers nervous, especially if they mistake it for smoke, flight attendants are trained to provide explanations and reassure passengers.

The fog in airplane cabins usually dissipates quickly because the cooler air warms up above the dew point, causing the fog to disappear within seconds. This natural phenomenon is harmless and common in certain conditions. Despite initial concerns, passengers can rest assured that fog in the cabin is a temporary and safe occurrence.