Humidity From Face Masks May Lessen the Severity of COVID-19

A Black woman wearing protective face mask buying grocery at a supermarket.

Luis Alvarez / Getty Images

Key Takeaways

  • A study from the National Institute of Diabetes and Digestive and Kidney Diseases suggests that wearing masks can lessen the severity of COVID-19.
  • If a person wears a mask, they are not only protecting others if they are sick, there are personal benefits as well.
  • Low levels of humidity have previously been linked with the spread of diseases like influenza.

While face masks were initially thought to only protect those around someone wearing a mask, public health officials have determined they also help keep mask-wearers from getting sick. Now a new study from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) found that wearing face masks not only slows down the transmission of COVID-19 but may lessen the severity of the virus as well.

The researchers tested four types of masks to see the level of humidity under the mask across three different temperatures: 8 °C (46.4 °F), 22 °C (71.6 °F), and 37 °C (98.6 °F). The four types of masks tested were:

  • Surgical masks
  • N95 masks
  • Light cloth masks
  • Heavy cotton masks

The level of humidity for no masks was also tested. Researchers found that heavy cotton masks had the highest level of humidity underneath; followed by N95s and light cloth masks, which had similar results; surgical masks; and finally, no masks. The February study was published in the Biophysical Journal.

"We propose that the increased humidity of inhaled air is a beneficial side effect to wearing masks, but the main purpose of masks during this pandemic has been to help slow transmission of COVID-19," the study's lead author Adriaan Bax, PhD, National Institute of Health Distinguished Investigator, tells Verywell.

How Humidity Slows Disease

Previous research has found that low levels of humidity can play a role in the increase of the spreading of disease. A 2007 study published in PLOS Pathogens found that the transmission of the influenza virus is increased during periods of lower levels of humidity. Humidity is often lower when it is colder out.

"There's a variety of reasons why we do get sick during the winter months," Robert L. Quigley, MD, DPhil, FACS, senior vice president and global medical director of health and security services firm International SOS, tells Verywell. "A lot of it has to do with close proximity we have with each other, but it's also because the relative humidity is low. The humidity will impact your immune response, and that is actually very relevant when it comes to COVID-19."

As indicated in the NIDDK study, high levels of humidity can trigger the mucociliary clearance (MCC) of pathogens from the lungs—a defense mechanism that removes mucus—both before and after an infection has occurred. "Effective mucociliary clearance can delay and reduce infection of the lower respiratory tract, thus mitigating disease severity," the authors wrote.

A 2017 article published in the Cold Spring Harbor Perspectives in Biology journal found that MCC is most efficient in 100% humidity and good core temperature. Under low temperature and humidity, ciliary cells decrease their activity and MCC slows down, increasing a person's risk of infection.

"You're much less likely to have the virus replicate in your cells and then advance down into the lower respiratory [area], as is the normal evolution of a COVID-19 infection," Quigley says. "So you want to stop it in its tracks in the upper airway." The mechanism from MCC can play a role in stopping the spread of the virus, according to Quigley.

While the amount of humidity in areas around the world varies during different times of the year, there will still be humidity under masks. "Even in a dry environment, the humidification generated by wearing a mask is quite high," Bax says. "If the environmental humidity were high, the additional increase generated by the mask may not add much additional benefit, whereas the discomfort to the wearer increases."

What This Means For You

If you wear a mask or two masks, you will likely have more humidity in your lungs. If you do contract COVID-19, the humidity may help trigger a response that could lessen the severity of the virus in your system.

Protecting Yourself and Others

As the COVID-19 pandemic continues to disrupt people's lives, Quigley says research justifying certain behaviors we have had to adapt to is important, since many are dealing with "pandemic fatigue."

"If you can provide me data that supports or justifies that I'm not only helping others, but I'm helping myself, you're going to get more people to buy into that and cooperate and be compliant, and we might actually save some lives," Quigley says.

But wearing masks is not enough to stop the spread of transmission. You should also be practicing other safety precautions like social distancing, avoiding unnecessary travel, and washing your hands frequently.

Consider Double-Masking

A study from the Centers for Disease Control and Prevention (CDC) recently found that double-masking can reduce a wearer's risk of exposure to COVID-19 by over 95%. Wearing two masks can also increase the humidity under a person's mask, according to Bax.

"Leakage caused by a poor fit is often the limiting factor in mask efficiency, both for filtration and humidification," Bax says. "So, yes, double-masking can potentially further increase the level of humidity of inhaled air, mostly because it improves the fit."

When it comes to properly wear a mask to reduce leakage, Bax recommends following the CDC's guidelines on proper mask-wearing, including:

  • Wear medical procedure masks, like surgical masks
  • Wear masks that fit snugly around the nose and chin with no large gaps at the side
  • Wear masks with breathable fabric, such as cotton
  • Wear masks with tightly woven fabric
  • Wear masks with two or three layers
  • Wear masks with inner filter pockets

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Courtney J, Bax A. Hydrating the respiratory tract: an alternative explanation why masks lower severity of COVID-19. Biophys J. 2021. doi:10.1016/j.bpj.2021.02.002

  2. Lowen AC, Mubareka S, Steel J, Palese P. Influenza virus transmission is dependent on relative humidity and temperature. Baric RS, ed. PLoS Pathog. 2007;3(10):e151. doi:10.1371/journal.ppat.0030151

  3. Bustamante-Marin X, Ostrowski L. Cilia and mucociliary clearance. Cold Spring Harb Perspect Biol. 2016;9(4):a028241. doi:10.1101/cshperspect.a028241

  4. Brooks J, Beezhold D, Noti J et al. Maximizing fit for cloth and medical procedure masks to improve performance and reduce SARS-CoV-2 transmission and exposure, 2021. MMWR Morb Mortal Wkly Rep 2021;70:254–257. doi:10.15585/mmwr.mm7007e1

  5. Centers for Disease Control and Prevention. Guidance for wearing masks.

By Julia Métraux
Julia Métraux is a health and culture writer specializing in disability.