During the novel coronavirus pneumonia epidemic, only one properly worn qualified medical mask is sufficient to achieve the desired protective effect in the general environment. Although multiple masks can theoretically increase the protective effect, this approach will increase the ventilation resistance, resulting in poor breathing, as well as increasing the discomfort of wearing them, which may not be worth the cost and has little substantive significance. In fact, for the protective effect of the mask, we need to focus more on its airtightness.