This article originally appeared on TravelAndLeisure.com.
The next time you go to turn off the ventilation above your seat on an airplane — whether because you're afraid of getting sick or you're downright chilly — you might want to reconsider.
Using that tiny vent can actually work to your advantage, as it can help you avoid contact with certain microorganisms that can get you sick during a flight.
Travel + Leisure spoke to Dr. Mark Gendreau — the medical director and vice chair of emergency medicine at Lahey Medical Center-Peabody, and an expert on the spread of infectious diseases associated with air travel — to learn how it works and how travelers can best utilize the that little air conditioner.
“Ventilation on airplanes has gotten a bad reputation, but it’s completely unfounded,” Gendreau told T+L.
Part of the reason for this, Gendreau explained, is that there wasn’t really any research on the topic until the last 15 years. But the other reason is a common misconception people often have about the way plane ventilation systems actually work.
“The flow pattern of air on an aircraft doesn’t necessarily work front to back, or back to front. It’s actually compartmentalized into various sections on the aircraft,” Gendreau said.
“As a rule of thumb, the air that you’re typically breathing and exposed to is usually anywhere from two to five rows surrounding your seat,” he added.
Here's how the ventilation systems work.
Each of these sections (known as temperature control zones), receives air from overhead distribution nozzles that flows through the length of the cabin. The air exits the plane through a grill that's often located beneath the windows, or where the side walls meet the floor of the plane.
This air then combines with the air outside before going through a HEPA (High Efficiency Particulate Air) to clear away dust and microbes before re-entering the plane.
The number of these ventilation zones varies depending on the aircraft, but each zone typically goes through this filtration process 15 to 30 times within the hour, with 50 percent of the air getting re-circulated and 50 percent of the air coming from outside, according to Gendreau.
The systems were primarily designed during the time when smoking was permitted on flights, Gendreau said, meaning airlines had to come up with an efficient and regular filtration system for their ventilation to clear the smoke from the cabins.
For this reason, HEPA filters can remove more than 99 percent of dust and microbes in the air, Gendreau said, though there are times where you'll want to turn to your personal vent.
“For airborne viruses, it is incredibly important to ventilate, since ventilation becomes your main means of control besides isolating the affected person,” Gendreau said.
Airborne viruses, like tuberculosis and measles, are transmitted by tiny droplet nuclei that can hang in the air for up to five hours, Gendreau said.
While viruses associated with the common cold and upper respiratory track infections tend to be larger in size and heavier (consequently falling to the floor rather quickly), these particles linger. Which is where your vent comes in.
By using the vent and turning it on medium or low, you can create an invisible air barrier around you that creates turbulence — simultaneously blocking these particles and forcing them to the ground faster.
Planes also have low humidity, which means your mucous membrane can dry out on during a flight. When this happens, you're more susceptible to contracting a virus, which is why keeping them away becomes all the more important.
And because those heavy common cold particles can still travel up to six feet every time you cough, sneeze, or speak, it’s equally important to wipe down and avoid touching surfaces (like that tray table you were probably resting your head on).