evidence: Mask Myths: Does a Mask Limit My Oxygen Intake? [...] Additionally, people of advanced age or weight do lose lung function and may find it more difficult to breathe with a mask on, but for most, it will not impair oxygenation (oxygen getting into the blood) or ventilation (blowing of carbon dioxide). Health care professionals have worn masks for decades, often uninterrupted for hours, in operating rooms without adverse effects. If you are unsure about your oxygen capacity speak to your health care provider. Should I wear a mask while exercising indoors/outdoors?