….air, once exhaled, is heated, humidified and charged with CO2. It becomes a perfect culture medium for infectious agents (bacteria, fungi, viruses). Studies have shown that the porosity (microscopic holes) of the masks allows exhaled germs to accumulate on the external surface of the mask. Not only do we re-inhale our own CO2, but by touching our mask all the time (an inevitable gesture), we spread germs everywhere! … A pharmaceutical analysis has shown that in masks for personal use, there are “staphylococci, streptococci, neisseria, bacilli which contribute to contaminatation…”
Hypoxia (lack of blood oxygenation) due to prolonged mask wear is common [2-3-4] in apparently healthy individuals. It is even worse when worn by people suffering from chronic respiratory insufficiencies, already hypoxemic and/or hypercapnic at baseline.
Cotton (cloth) masks worn by some people do not do any better  :
“Neither surgical masks nor cotton masks effectively filtered out CoV-2 SARS when infected patients coughed. It should be noted that we found greater contamination on the outside surfaces than on the inside surfaces of the masks.
In conclusion, surgical and cotton masks appear to be ineffective in preventing the spread of SARS-CoV-2 from the cough of COVID-19 patients to the environment and to the external surface of the mask. “COVID-19: Continuous Wearing of Mask Aggravates Risk of Infection. “Psychological Terrorism”? Centre for Research on Globalization