evidence: What to know - Wearing a mask is an additional prevention strategy that you can choose to further protect yourself and others. [...] Generally, masks can help act as a filter to reduce the number of germs you breathe in or out. Their effectiveness can vary against different viruses, for example, based on the size of the virus. When worn by a person who has a virus, masks can reduce the chances they spread it to others. Masks can also protect wearers from inhaling germs; this type of protection typically comes from better fitting masks (for example, N95 or KN95 respirators). There are many different types of masks that have varying abilities to block viruses depending on their design and how well they fit against your face. Cloth masks generally offer lower levels of protection to wearers, surgical/disposable masks usually offer more protection, international filtering facepiece respirators (like KN95 respirators) offer even more, and the most protective respirators are NIOSH Approved® filtering facepiece respirators (like N95® respirators).