In addition, the outer layer of the mask often accumulates a lot of dust and bacteria in the outside air, while the inner layer blocks the exhaled bacteria and saliva. Therefore, the two sides cannot be used alternately. At the same time, when not in use, the anti-haze mask should be folded and placed in a clean sealed bag, and the side close to the nose and mouth should be folded inward. Don't just put it in your pocket or hang it around your neck.