Face masks: yes or no?
• You will see news articles saying that you don’t need face masks as they are largely ineffective, or
that you shouldn’t buy face masks because caregivers need them.
• These statements cannot both be true! If face masks are ineffective why do caregivers need them?
• Well, both surgical face masks and N95 respirators are effective (ref 1)
– Surgical masks are filters, causing bacteria and droplets to be caught in a meshwork of
polypropylene. They are not rated for completely filtering out aerosolized viruses, i.e.
individual viruses in a small water shell. There is some evidence SARS-CoV-2 can be
aerosolized, but its mode of spread is mostly through larger droplets.
– Masks absorb 95% of exhaled droplets from infected people (ref 2).
– Masks reduce flu transmission within households by 60-80% (ref 3).
– Surgical masks are nearly as effective as N95 respirators in lab tests against aerosols (ref 4)
and clinical trials against influenza transmission (ref 5).
– Update 3/28: In the SARS epidemic, wearing face masks was more effective than washing
hands 10 times daily (ref 6).
– A T-shirt blocks 70% of virus-sized particles, which is better than nothing (ref 7).
References (1) nyti.ms/2GeMUMy (2) Pubmed 23505369 (3) Pubmed 19193267 (4) Pubmed 17096360 (5) Pubmed 19797474 (6) Pubmed 18042961
(7) Pubmed 24229526