Many governments have made nose and mouth covering or face masks compulsory for schoolchildren. The evidence base for this is weak.1,2 The question whether nose and mouth covering increases carbon dioxide in inhaled air is crucial.
The normal content of carbon dioxide in the open is about 0.04% by volume (ie, 400 ppm). A level of 0.2% by volume or 2000 ppm is the limit for closed rooms according to the German Federal Environmental Office, and everything beyond this level is unacceptable.
Children under normal conditions in schools wear such masks for a mean of 270 (interquartile range, 120-390) minutes.3 The Figure shows that the value of the child with the lowest carbon dioxide level was 3-fold greater than the limit of 0.2 % by volume.4 The youngest children had the highest values, with one 7-year-old child’s carbon dioxide level measured at 25 000 ppm.
This is because of the dead-space volume of the masks, which collects exhaled carbon dioxide quickly after a short time. This carbon dioxide mixes with fresh air and elevates the carbon dioxide content of inhaled air under the mask, and this was more pronounced in this study for younger children.
This leads in turn to impairments attributable to hypercapnia. A recent review6 concluded that there was ample evidence for adverse effects of wearing such masks. We suggest that decision-makers weigh the hard evidence produced by these experimental measurements accordingly, which suggest that children should not be forced to wear face masks.