A doctor in Ireland, tired of hearing people say masks will restrict their breathing, posted a video on Twitter in which he puts on six masks.

He does this while hooked up to a machine that measures oxygen levels in the blood.

The meter barely moves.

Getting asked

“Does wearing a face mask lower your oxygen levels” repeatedly by patients today!

Based on what they are reading on social media

*Face coverings / masks don’t reduce your oxygen levels!*

I managed to get six face masks on + it had no effect on my oxygen levels! pic.twitter.com/qNKYa8pejx

— Maitiu O Tuathail (@DrZeroCraic) July 14, 2020

The U.S. Centers for Disease Control has said while carbon dioxide can collect between a person’s face and mask, it won’t collect in dangerous amounts or cause oxygen deprivation.

There is anecdotal evidence wearing a face-covering during exercise or prolonged periods of exertion can impact a person’s quality of breathing, depending on the type of mask worn.