Medical masks wear 4 to 6 hours to replace once, ordinary masks wear 4 hours to replace once, when the mask is contaminated and broken need to be replaced in time. 1. Medical masks: medical masks usually refers to N95 masks and medical surgical masks, can effectively block viruses and bacteria invasion of the nose and mouth, generally used by health care workers. Wearing N95 masks is recommended to be replaced after 4 to 6 hours, and wearing medical surgical masks is recommended to be replaced after 4 hours. 2. Ordinary masks: the role of ordinary masks is to keep warm and air filtration, and can not block airborne viruses and bacteria, generally used by the general public, it is recommended to wear a replacement after 4 hours. 3. When the mask is contaminated by blood, body fluids, nasal secretions, when the mask is in close contact with the infected person, or when the mask is broken, it should be replaced in time to avoid infection. It is recommended that people choose the right mask according to their own situation and replace it according to the length of time they wear it. It is not recommended to wear a mask for a long time in order to avoid weakening the protective effect.