It's one of the first things most of us reach for to turn off whenever we board a flight, especially if it's on a chilly morning.
But this simple action could be causing more harm than good.
Dr. Mark Gendreau, medical director at Lahey Medical Center, has told Travel + Leisure that turning off the air vents makes us more susceptible to airborne viruses.
"For airborne viruses, it is incredibly important to ventilate, since ventilation becomes your main means of control besides isolating the affected person," he revealed.
When you turn on the air vent, it creates turbulence and an air barrier around you which blocks particles from reaching you and potentially making you sick.
These viruses that can linger in the air for hours include measles and tuberculosis, as well as the common cold and upper respiratory tract infection.
It's also common for people to think that by leaving the air vents on, it's spreading air around the plane as well as nasty bugs.
"Ventilation on airplanes has gotten a bad reputation, but it’s completely unfounded," Gendreau said.
"The flow pattern of air on an aircraft doesn’t necessarily work front to back, or back to front. It’s actually compartmentalised into various sections on the aircraft."