What is this button in the car for?

However,  in winter , this button can be problematic. Why? Because continuously recycling the same air increases  the humidity level  in the passenger compartment. This can lead to:

• Rapid fogging  of the windshield and windows , reducing your visibility
• A buildup of CO₂,  which can lead to fatigue, headaches or discomfort
• An environment conducive to the development of  mold and bacteria , harmful to health

And all this can happen without you even realizing it. You think you’re improving your comfort,  but you risk compromising your safety.