Do face masks reduce the flow of oxygen to the blood?

One of the most common myths about masks is the claim that masks reduce oxygen supplies, cause carbon dioxide "intoxication" and weaken your immune system. While masks may not be the most pleasant item to wear, they will definitely not deprive you of oxygen. But then, one may ask, how can team Hyjiva provide an unbiased take on masks.

Here’s how we’re gonna do it… We will reproduce the conclusions of the World Health Organization (WHO), American Lung Association, The Physiological Society (UK) and a study by researchers at McMaster University in Canada. We will also offer you a simple test that you could do at home.

In the end, you should have a pretty good idea if there is any truth to the claims of masks reducing oxygen levels.

Statement by WHO:

FACT: The prolonged use of medical masks when properly worn, DOES NOT cause CO2 intoxication nor oxygen deficiency

The prolonged use of medical masks can be uncomfortable. However, it does not lead to CO2 intoxication nor oxygen deficiency. While wearing a medical mask, make sure it fits properly and that it is tight enough to allow you to breathe normally. Do not re-use a disposable mask and always change it as soon as it gets damp.


Statement by American Lung Association:

Do Masks Cause Low Oxygen Levels?

Absolutely not. We wear masks all day long in the hospital. The masks are designed to be breathed through and there is no evidence that low oxygen levels occur. There is some evidence, however, that prolonged use of N-95 masks in patients with preexisting lung disease could cause some build-up of carbon dioxide levels in the body. People with preexisting lung problems should discuss mask wearing concerns with their health care providers. There is absolutely no scientific evidence that mask wearing or physical distancing weakens the immune system.


The Science - as explained by The Physiological Society:

Are face masks reducing the oxygen in your blood?

Paper face masks and fabric face coverings are permeable to air but restrict the movement of water droplets that we exhale or sneeze. The two key gases for respiration, oxygen and carbon dioxide, can move freely across these materials.

During normal breathing we inhale about 500 ml per breath. As we take approximately 12 breaths per minute, this amounts to about 6000 ml (6 litres) of air inhaled per minute. Not all the air, however, reaches the tiny sacs at the tips of the branching structures in our lungs, called the alveoli. This is where gas exchange with our blood takes place.

The air that stays in the conducting airways (trachea and bronchi) and does not make it to the site of gas exchange is called “anatomical dead space.” This is about 150 ml for each 500 ml breath. In other words, with each breath, only about 350 ml is available for gas exchange, meaning this is the amount that could make it to our tissues and help keep them healthy.

Theory governing gas transport in the body uses the partial pressure of oxygen in the atmosphere (the amount of oxygen compared to other gases), because this determines how much oxygen is available for our bodies.

The partial pressure of oxygen in the air is approximately 21 kPa if barometric pressure is 100 kPa which is usually the case around sea level. In other words, 21% of the air we breathe is oxygen, when we are not at high altitude. When we are at high altitude, this changes, as atmospheric pressure and thus oxygen partial pressure decrease.

Thus, 882 ml of oxygen per minute gets to the alveoli (350 ml x 12 breaths x 21%).

Our bodies generally use 250 ml of this oxygen per minute. What is left then mixes with the carbon dioxide (that is being released for exhalation) and water vapour, so the amount of oxygen at the alveoli (in this example) is approximately 15% (882- 250/ 350 x 12).

Oxygen in the blood equilibrates with oxygen in our alveoli. Blood is maximally saturated with oxygen when alveolar oxygen is 13-15%. This means this means that all the all the oxygen binding sites on haemoglobin (which makes our blood red) are occupied. So even if more oxygen were available, blood saturation with oxygen does not increase. Furthermore, the relationship between % oxygen and blood saturation is not linear, oxygen levels would need to halve to reduce saturation to 90%.

Increased activity requires more oxygen and so you breathe deeper and quicker, to maintain the saturation of your blood with oxygen.

What might a face mask do? There has been discussion that a face mask might add to anatomical dead space by extending it beyond the mouth area. If everything else stays the same, an extra 20 ml say, of dead space, theoretically will reduce the percentage of oxygen at the alveolus, but the effect is very small, meaning that blood still would stay fully saturated with oxygen.

Think about how many people go swimming with snorkels, how much dead space this adds and how it has remarkably little effect on our activities.

So, does a face mask restrict flow of air into the lungs? The bottom line is, if used correctly, it does not. If airflow is restricted, less millilitres of oxygen get to the alveoli, and less carbon dioxide is exhaled. While this reduces the percentage of oxygen in our lungs, and increases carbon dioxide, the body senses these changes in the lungs and stimulates breathing.

This means that you will take more breaths and blood oxygenation/saturation will be maintained. In other words, paper face masks and fabric face coverings do not affect blood oxygen saturation, so please spread the word and counter misinformation you see on the internet or hear in conversations.


Study by McMaster University in Canada

Peripheral Oxygen Saturation in Older Persons Wearing Nonmedical Face Masks in Community Settings

Fueled partly by claims on social media that masks can cause hypoxia and are therefore dangerous, concerns have emerged about the safety of wearing face masks. We examined whether wearing non-medical face masks was associated with a change in oxygen saturation.


This was a crossover study in which participants self-measured peripheral oxygen saturation (SpO2) before, while, and after wearing a mask. The study protocol was approved by the Hamilton Integrated Research Ethics Board. We included individuals aged 65 years or older and excluded those who had co-morbid cardiac or respiratory conditions that could lead to dyspnea or hypoxia at rest or who were unable to remove the mask without assistance.

To minimize variability, we provided participants with a 3-layer plane-shaped disposable non-medical face mask with ear loops and a portable pulse oximeter.


The pooled mean SpO2 was 96.1% before, 96.5% while, and 96.3% after wearing the mask. None of the participants’ SpO2 fell below 92% while wearing masks.


In this small crossover study, wearing a 3-layer non-medical face mask was not associated with a decline in oxygen saturation in older participants. These results do not support claims that wearing non-medical face masks in community settings is unsafe.


DIY Home Test

If you have access to a pulse oximeter, we recommend checking your SpO2 level before wearing a mask. Repeat this at different hourly intervals after you have worn a mask. Once you have established that there is no decline in oxygen saturation, do share your results with family and friends; and dispel any myths that may have been propagated in your social circles.