I agree studies show it can produce too much carbon monoxide in the lungs. Not sure if that proves why people have no brains though.
A research letter
published in JAMA Network by scientists from Poland, Germany and Austria stemmed from an analysis involving 45 children, who were 10 years old on average, with ages ranging from 6-17.
While open air consists of about 0.04% carbon dioxide by volume, the German Federal Environmental Office caps off acceptable carbon dioxide volume in closed rooms at 0.2% (2,000 ppm), authors wrote. To conduct the study, the team first measured baseline carbon dioxide levels without a mask for 3 minutes. For each mask, the team measured 3-minutes of carbon dioxide in both inhaled and exhaled air, 3-minutes of carbon dioxide content during inhalation and 3-minutes of carbon dioxide content during exhalation.
Results suggested levels of carbon dioxide exceeded acceptable levels after 3 minutes by a factor of 6; averages ranged between 13,120 and 13,910 parts per million (ppm) in inhaled air under surgical and filtering facepiece 2 (FFP2) masks.
“The youngest children had the highest values, with one 7-year-old child’s carbon dioxide level measured at 25,000 ppm," the letter reads. They noted kids wear masks in school for about 270 minutes on average, or 4.5 hours.