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Whether you have owned your car for a day or a decade, you have probably seen the air recirculation button on the dashboard. If you’re unsure which one it is, it’s the button with the diagram of a car and an arrow bent like a “U.” This icon represents that the air being blown into the car is recirculated through the cabin instead of coming from outside the car.

It works well when you must circulate cold air throughout the cabin on a hot day or hot air on a cold day. However, unbeknownst to many drivers, this little button can be a health hazard if used improperly.

When you shouldn’t use the air recirculation button in your car

The air recirculation button on a Honda S2000
The air recirculation button on a Honda S2000 | Joe Santos, MotorBiscuit

It’s normal to get into your car on a hot day and turn on the air conditioner to cool down the cabin. One thing to note is that the car will automatically turn the recirculation button on to circulate the cold air. However, it’s better to turn the recirculation function off for about 10 minutes and let the air circulate and the cabin cool before turning it back on.

Why? Because the air conditioner emits formaldehyde, which is hazardous to breathe in. The formaldehyde and other potential contaminants can clear out by airing the car first and not recirculating the air. Afterward, you can turn the recirculation function on.

Another time that recirculating the air in the car can be dangerous is during the wintertime. Recirculating hot air in the car when it’s cold outside can cause humidity and make the windows fog. As you can imagine, having foggy windows while driving can be hazardous.

When is the best time to recirculate the air in your car?

A man points to the climate control area in a Volkswagen.
An auto climate control button | via Getty Images

Although there are a couple of times when recirculating the air in your car is hazardous, there are many other times the function can be useful. According to Jerry, here are a few ideal times to press the button:

  • When the A/C is on: Provided that you have aired the car out properly for 10 minutes, you should press the recirculation button to circulate the air and keep the cabin cool.
  • In dense traffic: While sitting in traffic, your car will be in the middle of many others emitting harmful fumes. Pressing the recirculation button will keep the fumes out of the car.
  • During allergy season: Do you hate sneezing in your car? If so, be sure to keep the recirculation button pressed during the allergy season to keep the pollen out.
  • A dirt road: If you’re driving down a dirt road and don’t want all of that dust sitting in your car, press the button.
  • Driving on a smelly road: Are you driving on a road that’s passing cow pastures? If so, you don’t want that outside air coming in, so press the recirculation button.

How does the air recirculation button work?

The Max AC button on a Volkswagen
The max AC button | via Getty Images

When you press the air recirculation button on the dashboard, a little flap moves to cut off the outside air intake when the function is turned on. When you turn the button off, the flap opens up to let in the outside air. It’s important to use this button wisely to ensure that your health, or your car, is not compromised.