evidence: But do face masks really protect against the spread of infectious respiratory diseases, like SARS and COVID-19? And, if so, just how effective are they? [...] An expert consultation on the effectiveness of cloth masks published in early April 2020 indicated that the type of fabric used and its thickness could influence how well cloth masks work in preventing disease transmission. But the assessment also suggested that there are important trade-offs to consider. For example, thick fabrics or multiple layers of fabric are more likely to catch small aerosolized particles—the types of small particles sometimes trapped by surgical and more frequently by N95 masks—but they also are more difficult to wear, given their high degree of breathing resistance. A mask that is uncomfortable is likely to be pulled down or worn incorrectly, undermining its potential effectiveness. Of course, ultimately underlying the ability of face masks to prevent disease transmission is human behavior. Even if a mask is fundamentally effective in trapping infectious particles, it is still up to the individual to wear it properly. People must also be aware that if their cloth masks trap significant moisture, the masks need to be cleaned or disposed of to prevent viral contamination of surfaces.