Masking is not healthy. Masks, respirators any safety equipment really are used only when it is less safe to do something without them. Masks should not be worn all day, everyday. Even those whose jobs require masks, such a surgeons change theirs frequently. There may different lengths of time but the one I have repeatedly found is 4 hours. Change the mask or respirator filter/s every 4 hours. If you touch the filter or mask, change it immediately. They are health risks and should not be used except when the task requires them. Being made to force my students to wear masks in class while I know they are unhealthy is unethical. So to unemployment I go.