|Man in green mask delivering large box
As is often the case with this type of question, the correct answer is, “It depends.”
Viruses are spread in many ways. Some are airborne pathogens spread by droplets or particles, as from a sneeze, while others are transmitted through skin contact with infected surfaces. Obviously a face mask is not effective against viruses you pick up from touching doorknobs or water faucets after a flu patient has touched them. That is where proper hand washing comes in.
Face masks are commonly used to prevent infection by airborne droplets. They seem to be effective if worn by the infected person to prevent spreading the germs to others. But different types of masks have different levels of effectiveness in protecting non-infected individuals from becoming infected.
Reusable washable cloth masks have very low effectiveness and may actually become a source of infection. These are not recommended.
Disposable “surgical face masks” made of synthetic fibers, often colored blue or green, protect the wearer from large droplets. However, they do not fit tightly to the face, so smaller particles can be breathed in despite wearing the mask. Additionally, droplets from the mask wearer have been shown to escape around the edges of the mask. Taping the surgical face mask to a form-fitting molded facial moulage (personalized mask) is effective in limiting passage of airborne particles, so it is the loose fit of these masks that prevents their full effectiveness.
Single use N95 particulate filtering respirators are recommended for healthcare workers by the Centers for Disease Control to prevent exposure to droplet viral infection. The numeral 95 indicates that this type of mask removes 95% of small airborne particles. These masks fit tightly around the nose and mouth and users are required to have an annual fitting test to ensure their masks are being properly positioned for full protection. Although these masks are the most effective protection, they can be difficult to breathe through while worn. These products can be purchased by the general public, but are not recommended for ordinary use, especially by persons with respiratory or cardiac conditions. They do not work for children or persons with facial hair.
Research has also shown that in households with a child with influenza-like illness, adults were likely to wear any type of face mask less than half the time, even though adherence to mask use was shown to reduce the risk of developing the same disease. If obtained and not worn properly, face masks are ineffective in stopping the spread of flu viruses. People are more likely to wear face masks if they perceive they are highly susceptible to severe life-threatening infections.