Most people who take measures to safeguard themselves under specific conditions use N95 Respirators to achieve this goal. These devices provide a physical barrier to pathogens that would enter the nasal or buccal cavity freely otherwise. From there, these harmful organisms would have proceeded to the lungs and other areas within the body where they would cause illness and even death. In some sectors, prefer them and ensure that the gear is worn even if safety regulations do not force compliance.
N95 Respirator (mask)-via Wikimedia, CCA 1.0 by AlamosaCountyPublicHealth
People who use this equipment to keep safe should remember that it is not a hundred percent effective against all harmful particles, whether these are organic or inorganic. You cannot totally trust a mask to protect you under any conditions. The Center for Disease Control reminds users that the N95 Respirator products filter over ninety percent of airborne substances but it cannot catch them all.