Face masks may limit the severity of coronavirus cases, University of California San Francisco researchers said in a paper published in the Journal of General Internal Medicine.

Although face coverings are more effective in preventing droplets from being expelled into the air than they are in preventing droplets from being breathed in, masks still may be able to mitigate how severe an illness an individual gets if infected by COVID-19, researchers explained in the release.


“It’s likely that face masks, by blocking even some of the virus-carrying droplets you inhale, can reduce your risk of falling seriously ill from COVID-19," Monica Gandhi, MD, an infectious disease specialist at UC San Francisco, said in a university press release. “The more virus you get into your body, the [sicker] you are likely to get."

Based on the researchers’ epidemiological observations, Gandhi and her colleagues suggest in the paper that masks can lead to milder or asymptomatic infections by reducing the amount of virus people breathe in.

"Masks, depending on [the] type, filter out the majority of viral particles, but not all," the researchers stated in the published report.

The notion of viral dose or viral inoculum was incorporated with early smallpox vaccines in the 16th century in China where small amounts of the virus were injected into a healthy person to create a mild illness followed by immunity. It was also involved with the influenza A virus, where healthy volunteers who received a larger dose of the influenza A virus had symptoms that were more severe, the release said.

"Masks, depending on [the] type, filter out the majority of viral particles, but not all," the researchers stated in the published report. (iStock)

The study authors credit face masks for contributing to lower death rates and more mild cases with the more recent wave of COVID-19 infections, along with better treatments, more testing, and younger patients, according to the press release. However, more data is needed to track cases geographically and correlate the severity with mask-wearing.

Severe illness rates are lower in countries such as Singapore, Japan, Taiwan, Thailand, and South Korea where the wearing of face masks was already socially acceptable, according to the release.

“We’re also saying that masks, which filter out a majority of viral particles, can lead to less severe infection if you do get one,” Gandhi stated in the press release. “If you get infected, but have no symptoms – that’s the best way you can ever get a virus.”

The release noted a hamster study where a surgical mask separated cages of hamsters with COVID-19 and uninfected hamsters. The mask was found to decrease transmission of coronavirus, while the hamsters that had contracted SARS-CoV-2 developed milder symptoms, according to the report.

Gandhi said viral dose could be another factor regarding the prognosis of the virus based on two outbreaks of coronavirus on cruise ships, according to the release. The first outbreak of SARS-CoV-2 on the Diamond Princess outside of China 18% of the 634 passengers positive for COVID-19 were asymptomatic. In the other case, in March onboard an Argentinian cruise ship, 81% of the 128 people who tested positive were asymptomatic, according to the news release.

The major difference, according to Gandhi, was that passengers on the Argentinian ship were given surgical masks and staff N95 masks as soon as a passenger was detected to have COVID-19.


There were similar findings in food processing plants, per the researchers. Some 95% of 124 infected employees were asymptomatic in an Oregan seafood processing plant, while nearly 95% of 481 COVID-19-positive employees were asymptomatic in a Tyson chicken processing plant in Arkansas where masks were worn.

Wearing face masks could result in less severe cases of COVID-19 which would put less of a burden on the health care system and possibly increase herd immunity as a potential vaccine is developed, Gandhi said in the release.