The white smoke seen inside an airplane cabin before takeoff is caused by the air conditioning system. When the aircraft is pressurized with atmospheric air before takeoff, the warm and humid air from outside is almost saturated with moisture and is very close to the dew point. After the first pressurization, the cold air blown by the air conditioning system cools the ventilation point areas, and the invisible gas and water vapor in the region of sudden temperature drop turns into visible water droplets, which appear as white smoke near the AC vents. This phenomenon is a normal process that occurs inside an aircraft before takeoff and is not a cause for concern. The cabin crew does not pay attention to it because it is a common occurrence.