Could wearing a mask for long periods be detrimental to health?

Retired neurosurgeon Dr. Russell Blaylock has highlighted a number of studies linking prolonged mask use to headaches and lowered blood oxygen levels, which can weaken the immune system.

A man wears a face mask  with David Star at the Nachlaot Neighborhood in Jerusalem on April 12, 2020. A full closure on 17 Jerusalem Neighborhoods went into effect today at noon in efforts to contain the spread of the coronavirus. (photo credit: NATI SHOCHAT/FLASH 90)
A man wears a face mask with David Star at the Nachlaot Neighborhood in Jerusalem on April 12, 2020. A full closure on 17 Jerusalem Neighborhoods went into effect today at noon in efforts to contain the spread of the coronavirus.
(photo credit: NATI SHOCHAT/FLASH 90)
Could the requirement to wear masks in public to prevent the spread of the coronavirus be doing more harm than good to people's health?
A retired neurosurgeon believes so, pointing toward studies which found that wearing masks for prolonged periods can cause serious side effects.
In an article published by Technocracy News, Dr. Russell Blaylock wrote that the side effects from prolonged wearing of a face mask "can vary from headaches to increased airway resistance, carbon dioxide accumulation, to hypoxia, all the way to serious life-threatening complications."
The side effects vary depending on whether they are cloth or paper surgical masks or N95 respirator masks because the N95, being a more effective filter, also limits breathing to a greater degree, and is therefore more commonly associated with headaches, Blaylock reported.
He highlighted one study of 212 healthcare workers who were asked to report on the presence of headaches while using the N95 mask, including the duration of the headache, the type of headache, and whether they had pre-existing headaches. The study found that around a third of workers developed headaches when using the N95 mask, the majority had pre-existing headaches that were made worse by the use of the mask, and around three in five required pain medication to relieve the headache.
And although tight straps or pressure from the mask were considered as potential causes, the evidence pointed to the headaches being caused by reduced blood oxygenation, or an increase in carbon dioxide in the blood.
"It is known that the N95 mask, if worn for hours, can reduce blood oxygenation as much as 20%," Blaylock wrote. This, he said, "can lead to a loss of consciousness, as happened to the hapless fellow driving around alone in his car wearing an N95 mask, causing him to pass out, and to crash his car and sustain injuries. I am sure that we have several cases of elderly individuals or any person with poor lung function passing out, hitting their head. This, of course, can lead to death."
A more recent study of 159 healthcare workers between the ages of 21 and 35 found that 81% developed headaches through the use of face masks, to the level at which their work performance was affected.
A third study measured the blood oxygen of 53 surgeons using an oximeter before and after surgery.
"The researchers found that the mask reduced the blood oxygen levels (pa02) significantly. The longer the duration of wearing the mask, the greater the fall in blood oxygen levels," Blaylock wrote.
The potential for masks to reduce oxygen levels in the wearer are important not only because this can lead to passing out, but also because they have been linked to reduced natural immunity. 
"In essence, your mask may very well put you at an increased risk of infections, and if so, having a much worse outcome," he wrote.
Little is definitively known about how effective the use of masks is in controlling the spread of COVID-19 because no studies have yet been carried out specifically connecting the coronavirus to mask use.
From the outset of the pandemic, it has been assumed that the coronavirus behaves like other respiratory viruses in terms of spread as well as symptoms. However, Blaylock points to a 2012 study titled, "The use of masks and respirators to prevent transmission of influenza: A systematic review of the scientific evidence," which looked at 17 of the best studies in the field and concluded: "None of the studies established a conclusive relationship between mask/respirator use and protection against influenza infection.”
He also highlights that both the Center for Disease Control and Prevention (CDC) and the World Health Organization initially recommended that only those already known to be infected with the coronavirus need wear a mask, to minimize spreading it to others, a policy which is also considered good practice regarding other diseases.
"When a person has TB we have them wear a mask, not the entire community of non-infected," Blaylock wrote. "The recommendations by the CDC and the WHO [for everyone to wear a mask] are not based on any studies of this virus and have never been used to contain any other virus pandemic or epidemic in history."
The current advice given on the WHO's website is still not to use masks unless you have the virus and are at risk of infecting others, or looking after those who may be infected with coronavirus.
An information video by the organization titled, "Can wearing a mask protect you against coronavirus?" advises: "Medical masks cannot protect against the new coronavirus when used alone. When you use them, you must combine with hand hygiene and other preventative measures.
"WHO only recommends the use of masks in specific cases," the video continues. "If you have a cough, fever and difficulty breathing, you should wear a mask and seek medical care. If you do not have these symptoms, you do not have to wear masks because there is no evidence that they protect people who are not sick."
It is currently a requirement to wear a mask while in public spaces in Israel.