The disadvantage of a mask with an exhalation valve is that the breath exhaled by the wearer will not pass through the filter material. Therefore, people who have developed respiratory symptoms or colds should not wear a mask with an exhalation valve, otherwise people around them may be at risk of infection.
Medical staff usually wear sterilization masks without an exhalation valve. The medical staff themselves are also a high-risk group of infection. "Assuming this medical nurse has been infected, he himself will become a communicator."
The higher the risk of becoming a patient, the less suitable it is to wear a sterilization mask with an exhalation valve. In the same way, people who are in self-isolation should not wear masks with exhalation valves.