Mask Facts - they don't work

Association of American Physicians

The theory behind mask wearing:

Source control: Cloth mask can trap droplets that come out of a person’s mouth when they cough or sneeze.
Protection: Personal Protective Equipment (PPE) – only N95 masks

Note: A COVID-19 (SARS-CoV-2) particle is 0.125 micrometers/microns (µm); influenza virus size is 0.08 – 0.12 µm; a human hair is about 150 µm.

Virus is transmitted through respiratory droplets produced when an infected person coughs, sneezes, or talks.

A surgical mask is not a respirator. It cannot be used to protect workers who perform or assist with aerosol-generating procedures, which may create very fine aerosol sprays. A surgical mask can only be used to protect workers from contact with the large droplets made by patients when they cough, sneeze, talk or breathe.

Filter efficiency was measured across a wide range of small particle sizes (0.02 to 1 µm) at 33 and 99 L/min.
All the cloth masks and materials had near zero efficiency at 0.3 µm, a particle size that easily penetrates into the lung (SARS-CoV-2 is 0.125 µm)
Efficiency for the entire range of particles
T-shirts — 10%
Scarves — 10% to 20%
Cloth masks — 10% to 30%
Sweatshirts — 20% to 40%
Towels — 40%

Conclusion: Wearing masks (other than N95) will not be effective at preventing SARS-CoV-2 transmission, whether worn as source control or as PPE.