There are a lot of misconceptions about the supposed harm that comes from wearing masks as seen in protests at civic meetings and incidents at supermarkets — chiefly that wearing them reduces intake of oxygen or can lead to carbon dioxide poisoning. Here comes the science.
Jay, a registered nurse from Oakland, gives a demonstration with a pulse oximetry sensor, showing that even with three surgical masks there was no significant change in his oxygen saturation levels. He also measures whether wearing three masks will cause dangerous "carbon dioxide retention." The answer is pretty explicitly no.
"Wear your mask. You do not have a reason to not wear a mask, at all," he concludes.