evidence: MYTH: Wearing a mask causes you to inhale too much carbon dioxide, which can make you sick. FACT: Wearing a cloth mask will not cause dizziness, lightheadedness, and headaches (also known as hypercapnia or carbon dioxide toxicity). Carbon dioxide passes through the mask, it does not build up inside the mask. If you feel dizzy or get a headache, you may be dehydrated since wearing a mask doesn’t make it as easy to drink water. We recommend keeping yourself very hydrated. [...] FACT: This is not true. Wearing a face mask does greatly reduce the spread of infectious droplets from entering your mouth or nose when you’re around individuals who may be sick, but it doesn’t prevent all microbes from entering your body. If surgeons had weakened immune systems after wearing masks for hours, none of them would live past 50.