My study, based on the U.S. state of Kansas, provides the answer: case mortality was significantly lower in counties without mandatory masks. Mandatory masking increased case mortality there by 85%. Even after factoring in the reduced number of cases due to masks, the numbers still remain 52% higher. Over 95% of this effect can only be attributed to COVID-19, so it is not CO2, bacteria or fungi under the mask.
The reason for this is what I call the Foegen effect: deep re-inhalation of condensed droplets or pure virions which were trapped in the mask as droplets can worsen the prognosis. Each of these steps has been documented in the literature.
Two other, even larger evaluations show the same effect on the case fatality rate. A peer-reviewed study in the journal Cureus shows that there is no association between mask compliance and case numbers in Europe, but there is a statistically significant positive association between mask compliance and deaths. This means: more mask use, same number of cases, but more deaths.
My study is open access and you can find it here – the PDF version (available via the download button in the left bar) is particularly recommended for its helpful layout.The Foegen Effect: Why Face Masks Increase the Death Rate of COVID-19 – Rights and Freedoms