No matter what type of mask, there is a service life, and the mask needs to be replaced in time after reaching the service life. Due to the different concentration and nature of environmental particles, the different particle capacity of various masks as well as the use habits, storage methods and other factors can affect the service life of the mask, while there is a risk of bacterial and viral contamination. Therefore, it is recommended that masks be replaced regularly, preferably once every 2-4 hours. If the mask is deformed, wet or dirty, resulting in reduced protective performance, it is also necessary to replace the mask in a timely manner.