Researchers have found that wearing a mask increases the humidity of the air a person breathes in.

They suggest this may explain why mask-wearing has links with reduced COVID-19 severity.

The research, which appears in the Biophysical Journal, adds further evidence for the value of wearing masks.

Do masks reduce COVID-19 severity?

Face masks have been a crucial non-pharmaceutical intervention in the COVID-19 pandemic. Researchers believe they reduce the chances of a person passing the virus to another person, as well as acquiring the virus themselves.

Further, while healthcare professionals continue administering effective vaccines around the world, mask-wearing is still necessary.

The Centers for Disease Control and Prevention (CDC) point out there is not yet enough information on how these vaccines work in the real-world to recommend people stop wearing masks, even for those who have received two doses of the vaccines.

Recent research, which appears in the Journal of General Internal Medicine and the New England Journal of Medicine, found that face masks effectively reduce SARS-CoV-2 transmission and may also reduce its severity.

The researchers behind the articles suggest this is due to mask-wearers likely having exposure to reduced amounts of the virus. However, other scientists have contested this finding.

The researchers behind the present study are also skeptical that exposure to a small amount of the virus may account for a mask-wearer to have a less severe case of COVID-19.

Instead, they suggest the answer may lie in the humidity of the air that a person breathes while wearing a mask.

Humidity and disease severity

The researchers note that respiratory viruses, such as the common cold and influenza, often follow a seasonal pattern, with an increase in cases during the winter months. Some evidence also suggests this holds true with COVID-19.

Many factors may account for this, such as:

  • people spending more time indoors, where aerosols containing the virus can build up
  • people with a vitamin D deficiency
  • lower general levels of ultraviolet light, which may inactivate the virus
  • the virus being able to last longer in colder, less humid air

The researchers also point out that cold, less humid air can affect the physiology of the organism a virus might infect, inducing more severe infections. For example, researchers found that mice in low humidity developed more severe cases of influenza.

The researchers suggest that increased humidity may reduce the dehydration of a person’s lungs that can often occur during cold weather. They also believe increased humidity may improve a person’s mucociliary clearance — the way the lungs remove mucus and harmful particles.

Both of these could mean a reduction in the severity of a COVID-19 infection.

As a result, the researchers wanted to see whether the reduction in disease severity associated with mask-wearing could, in principle, be explained by masks increasing the humidity of the air a person breathes.

Mask types tested

To find out if masks increase the humidity of the air a person breathes, the researchers asked participants to breathe into a sealed steel box wearing one of four common types of mask:

  • N-95 respirator
  • surgical mask
  • cotton-polyester mask
  • heavy cotton mask

The researchers then measured the box’s humidity, comparing this to the humidity measured when a person breathed into the box without wearing a mask.

This told the researchers how much moisture was being trapped by the mask, condensing on the inside of the mask and then evaporating and entering a person’s lungs as they inhaled.

The scientists carried out the test at three temperatures between 46–98oF (8–37°C).

Medical reference: Medical News Today