evidence: "Mask wearing allows us to open the economy up faster. Not wearing a mask around others only worsens the pandemic, leads to more disease, and worsens the economic effects." Do Masks Cause Low Oxygen Levels? Absolutely not. We wear masks all day long in the hospital. The masks are designed to be breathed through and there is no evidence that low oxygen levels occur. There is some evidence, however, that prolonged use of N-95 masks in patients with preexisting lung disease could cause some build-up of carbon dioxide levels in the body. People with preexisting lung problems should discuss mask wearing concerns with their health care providers. There is absolutely no scientific evidence that mask wearing or physical distancing weakens the immune system.