TORONTO -- A doctor in Ireland has made a video that appears to debunk the notion that wearing a face mask can lower a person’s oxygen levels.

In a 70-second video posted to Twitter on July 14, Dr. Maitiu O Tuathail, whose Twitter and LinkedIn profiles state he is a general practitioner based in Dublin, Ireland, is seen standing next to a machine that measures oxygen saturation levels in the blood. With a monitor clip over one of his index fingers, Tuathail is seen putting on a disposable medical mask.

Over the course of the short video, the doctor carefully puts on six masks in total, one at a time. As he does this, the meter steadily shows an almost-perfect oxygen saturation level that fluctuates slightly between 98 and 99 per cent.

In the post, which has been liked and retweeted thousands of times, Tuathail said he was repeatedly asked by patients if wearing a face mask would lower their oxygen levels. He said his patients were being misinformed and were basing their questions “on what they are reading on social media.”

“I managed to get six face masks on + it had no effect on my oxygen levels!” wrote Tuathail.

Questions and debate about whether face coverings can lower your oxygen levels and do more harm than good have been circulating online ever since face masks became mandatory in places around the world as a precautionary measure to limit the spread of the coronavirus.

In an article published on June 22 by Hartford HealthCare in Connecticut on the question of the possible dangers of wearing a face mask, a representative from the U.S.’s Centers for Disease Control and Prevention (CDC) said that while carbon dioxide can collect between a person’s face and mask, it won’t collect in dangerous amounts or cause hypoxia (oxygen deprivation), as some unsubstantiated theories suggest. The World Health Organization has also debunked the claim that prolonged use of a medical mask can cause CO2 intoxication or hypoxia.

The fact that Tuathail was stationary and not moving around was also questioned in some responses to his post from people who believe wearing a face covering during exercise or rigorous activity can impact breathing and levels of oxygen.

Informal experiments being conducted by researchers and scientists, as outlined in this New York Times article from June 17, does present some anectodal evidence that 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.

However, there is no clear scientific evidence that suggests a healthy person will suffer from wearing a face mask during non-rigorous activities, like walking or grocery shopping.

Canada’s public health agency, as well as the CDC, recommend the use of a non-medical face covering as an important step in slowing the spread of COVID-19 when combined regular preventive actions like hand-washing and physical distancing in public settings.