Information about wearing facemasks to prevent Covid-19 is becoming confusing…
WHO: Masks don’t prevent Covid-19.
Surgeon Gen.: Not for healthy people.
Health workers: We need more masks!
CDC in March: Not for general public.
CDC in April: Everyone should wear outdoors.
What studies say
“Penetration of cloth masks by particles was almost 97% and medical masks 44%,” according to a 2015 study on influenza-like illnesses.
A 2011 analysis of multiple studies of physical measures for reducing the spread of respiratory viruses showed masks were the best type. They help when the wearer is ill.
Interesting that the same 2011 analysis reports “Antiviral drugs and vaccinations may be insufficient to prevent their spread.” and “there was limited evidence that social distancing was effective”
Carbon Dioxide buildup?
Rebreathing carbon dioxide when using respiratory protective devices can result in fatigue, dizziness, headache and drowsiness, a 2013 study stated. Of course those symptoms are better than getting a virus, but the report goes on to say the topic is “relatively under researched.”
A 2014 study of one-hour use of N95 masks showed minimal increases in heart rate, respirator rate and transcutaneous carbon dioxide and oxygen saturation.
Tips for wearing facemasks from Harmony Lab. (not affiliated with this site)
Cloth face coverings should not be placed on young children under age 2, anyone who has trouble breathing, or is unconscious, incapacitated or otherwise unable to remove the mask without assistance.CDC
Disclaimer: The above is not considered health advice. More debate at Scientific American.