The WHO report ‘Recommendations on the use of masks in the context of IDVC-19. Provisional guidelines’distinguishes five different scenarios based on a classification by situation and type of environment, and ends up recommending the type of mask to be used in each of them.

This is the classification:

Situation or environment: In the area of confirmed or suspected widespread transmission, there are no or no other containment measures, such as physical distance, location of contact, appropriate testing, isolation and care of suspected and confirmed cases.
Population: The general population in a public setting, such as supermarkets, workplaces, social gatherings, mass meetings, closed environments, including schools, churches, mosques, etc.
Purpose of using the mask: The possible benefits of source code control.
Suitable mask type: Hygienic masks.

Situation or setting: Densely populated locations where physical distance cannot be reached; monitoring and epidemiological testing capabilities; and limited means of isolation and quarantine.
Population: People living in crowded environments and specific settings, such as refugee camps, camps, slums.
Purpose of mask use: The potential benefits of source code control.
Suitable type of mask: Hygienic masks.

Situation or environment: An environment where physical distance cannot be reached (close contact)
Population: The specific working conditions of the public who take public transport (such as buses, planes and trains) allow employees to have actual or potential close contact with others (such as social workers, cashiers, waiters (waiters, waitresses))
Purpose of using the mask: The possible benefits of source code control.
Suitable mask type: Hygienic masks.

Situation or environment: It is impossible to achieve an environment in which the body is alienated and the risk of infection or adverse consequences is increased.
Population: Vulnerable groups: -People ≥ 60 years old -People with accompanying diseases, such as cardiovascular disease or mellitus diabetes, chronic lung disease, cancer, cerebrovascular disease, immunosuppression.
Purpose of mask use: protection.
Suitable mask type: Medical mask.

Situation or setting: Any community setting.
Population: People who have any symptoms indicating COVID-19.
Purpose of mask use: Source of control.
Suitable type of mask: Medical mask.