An Irish doctor set out to debunk the myth that wearing a face mask lowers your oxygen levels and may cause brain damage as a result.

Maitiu O Tuathail, a general practitioner, conducted his experiment to allay the fears of his patients who were concerned about the dangers of face masks after officials made wearing them mandatory on public transport and in shops.

According to Insider, he filmed himself testing his oxygen levels while wearing not one, but six, masks at the same time. His oxygen level measured an excellent 99% as he put on as many masks as his ears could handle.

“That’s consistent whether you wear six masks for one minute or the entire day,” O Tuathail said, according to Insider. He added that oxygen molecules are so small they can permeate whatever you put on your face.

The Centers for Disease Control and Prevention said that “cloth face coverings are a critical tool in the fight against COVID-19 that could reduce the spread of disease,” in an editorial published last week.

“We are not defenseless against COVID-19,” said CDC Director Dr. Robert Redfield. “Cloth face coverings are one of the most powerful weapons we have to slow and stop the spread of the virus — particularly when used universally in a community setting.”

As far as excuses not to don a mask, at least one of them has been discredited. We now know that wearing a mask — or even six of them — won’t cut down your oxygen levels or damage your brain thanks to O Tuathail’s experiment.