Mask in the premise of keeping clean, the time to change the new time to wear the length of time shall prevail. Different levels of masks have different use times. According to the recommended use time on the outer packaging of masks, disposable medical masks and medical surgical masks are generally 4~6 hours, and medical protective masks are 6~8 hours. According to the "Guidelines for Wearing Masks for the Public and Key Occupational Groups (August 2021 Edition)", it is recommended that the cumulative wearing time of each mask should not exceed 8 hours; in addition, when the mask is dirty, deformed, damaged, or smells bad, it needs to be replaced in a timely manner.