1. The mask is contaminated, such as blood stains or droplets and other foreign objects.
2. The user feels that the breathing resistance becomes greater.
3. The mask is damaged.
4. Dust-proof filter cotton, when the mask is in good contact with the user's face, when the user feels a great breathing resistance, it means that the filter cotton is already covered with dust particles and a new mask should be replaced.
5. The anti-virus filter box, when the mask is in good contact with the user's face, when the user smells toxic substances, it should be replaced with a new one.
6. Ordinary mask wearing: activated carbon mask can generally be used for 2 days, n95 can be used for one week. If the mask has not been worn for a long time after cleaning, it is better to re-clean it before wearing it.