A surgical mask, also known by other names such as a medical face mask or procedure mask, is a personal protective equipment used by healthcare professionals that serves as a mechanical barrier that interferes with direct airflow in and out of respiratory orifices (i.e. nose and mouth). This helps reduce airborne transmission of pathogens and other aerosolized contaminants between the wearer and nearby people via respiratory droplets ejected when sneezing, coughing, forceful expiration or unintentionally spitting when talking, etc. Surgical masks may be labeled as surgical, isolation, dental or medical procedure masks. Although the material of which surgical masks are made will filter out some viruses and bacteria by trapping the aerosol suspended in breathed air, they only provide partial protection from airborne diseases because of the typically loose fit between the mask edges and the wearer's face. Surgical masks are distinct from filtering respirators, such as those made to the American N95 standard, which are more airtight and purposefully designed to protect against finer airborne particles. Evidence from randomized controlled trials that surgical masks reduce infection from diseases such as influenza is weak. Although a recent very large (over 300,000 people) study found some evidence that they reduced transmission in the community, surgical masks can vary greatly in quality which may make these studies less useful. The effect of surgical masks is partially attributed to filtering out some of aerosol particles that are how airborne diseases are transmitted. Surgical masks are highly variable but the material of which they are made typically filter out more aerosol particles than do cloth masks but much less than does the material of which N95, FFP2 and similar masks, are made. This combined with the poor fit suggests that surgical masks offer some protection to airborne diseases such as COVID-19 but less than do N95, FFP2 and similar masks. There are standards for the materials masks are made from. For example, the European EN 14683 Type II standard requires the material of the mask to filter particles (mean diameter close to 3 micrometres) containing the bacterium Staphylococcus aureus. The bacterial filtration efficiency of the mask material is the fractional reduction in the number of colony-forming units (CFUs) when the aerosol is passed through the material. For a Type II mask under this standard, the material must filter enough of the aerosol particles containing the bacteria to achieve a CFU reduction of at least