2, disposable masks tend to accumulate a lot of dust in the outside air, bacteria and other dirt, while the inner layer blocks the exhaled bacteria, saliva, therefore, the two sides can not be used alternately.
3, otherwise it will be the outer layer of contaminated dirt in the direct close to the face when inhaled into the body, and become a source of infection. Mask when not wearing, should be folded into a clean envelope, and will be close to the mouth and nose side inward folded, do not just stuffed into the pocket or hanging around the neck.