Today the Journal JAMA Pediatrics published a study which looked at the impact of masks on children. The study was led by a researcher in Poland who was joined by six other doctors from Germany and Austria. The researchers concluded there was a significant build up of carbon dioxide in children using masks, to levels that are well beyond what is considered healthy for indoor air by the German government.

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.

Looking at this Wikipedia article, it appears that acceptable concentrations of CO2 for indoor air vary quite a bit around the world:

The USA National Institute for Occupational Safety and Health (NIOSH) considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation.^[31] The UK standards for schools say that carbon dioxide in all teaching and learning spaces, when measured at seated head height and averaged over the whole day should not exceed 1,500 ppm. The whole day refers to normal school hours (i.e. 9:00am to 3:30pm) and includes unoccupied periods such as lunch breaks. In Hong Kong, the EPD established indoor air quality objectives for office buildings and public places in which a carbon dioxide level below 1,000 ppm is considered to be good.^[32] European standards limit carbon dioxide to 3,500 ppm. OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes. These higher limits are concerned with avoiding loss of consciousness (fainting), and do not address impaired cognitive performance and energy, which begin to occur at lower concentrations of carbon dioxide.

So here’s what the study of children wearing masks actually found [emphasis added]:

The mean (SD) age of the children was 10.7 (2.6) years (range, 6-17 years), and there were 20 girls and 25 boys. Measurement results are presented in the Table. We checked potential associations with outcome. Only age was associated with carbon dioxide content in inhaled air (y = 1.9867 – 0.0555 × x; r = –0.39; P = .008; Figure). Hence, we added age as a continuous covariate to the model. This revealed an association (partial η2 = 0.43; P < .001). Contrasts showed that this was attributable to the difference between the baseline value and the values of both masks jointly. Contrasts between the 2 types of masks were not significant. We measured means (SDs) between 13 120 (384) and 13 910 (374) ppm of carbon dioxide in inhaled air under surgical and filtering facepiece 2 (FFP2) masks, which is higher than what is already deemed unacceptable by the German Federal Environmental Office by a factor of 6. This was a value reached after 3 minutes of measurement. 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.

In the discussion section, the researchers conclude that complaints reported in a previous survey of thousands of German parents (kids experiencing headaches, difficultly concentrating, drowsiness, etc.) could be explained by the elevated CO2 levels. The study concludes: “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.”

The caveats here are that this study was very small, only a few dozen kids. Assume there will be some pushback from other doctors but as of now it’s brand new so there haven’t been any responses to it yet.