evidence: People do report feelings of discomfort, such shortness of breath, when they engage in physical activity while using face masks. But unlike long COVID symptoms, these feelings dissipate when they take off the masks. When researchers have measured physiological changes related to wearing masks, such as the concentration of oxygen or carbon dioxide in the blood, the effects have been minimal. [...] Nor is it the first time the authors of the review have claimed face masks could have harmful effects. Several of the authors speculated in a review published in March that masks might have caused stillbirths and other health issues. But this was an extrapolation based on studies exposing animals to carbon dioxide — and ignored the fact that masks don’t increase levels of the gas in humans in any clinically meaningful way. The Daily Mail nevertheless covered the paper in a story with an alarming headline, screenshots of which have been widely shared on social media. [...] Gideon M.-K; Health Nerd. "Face Masks Are Safe To Wear." Medium. 17 Apr 2023.