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For months, researchers have known that wearing a mask can help prevent people from spreading COVID-19. But new studies and updated guidance from the Centers for Disease Control and Prevention (CDC) now suggest that face masks protect the wearer too.

Masks block the virus from reaching a person’s mouth or nose, reducing the risk of infection by as much as 65 percent, according to one study. But even if viral particles get through this barrier, the disease may end up milder with less severe symptoms.

That’s the conclusion from a new paper to be published in the Journal of General Internal Medicine. The authors contend that people who wear face masks and have been exposed to COVID-19 will take in fewer coronavirus particles, putting less of a strain on their immune systems.

The research looks at animal experiments and indirect evidence from various events during the pandemic, mostly involving infected people who didn’t show any symptoms. When some people wear masks, the proportion of these asymptomatic cases dramatically rises. According to Dr. Monica Gandhi, an infectious disease physician at the University of California, San Francisco and an author of the paper, these trends of asymptomatic cases suggest that mask-wearing doesn’t completely shield you from disease but makes that disease milder, potentially reducing hospitalizations and deaths.

For example, Dr. Gandhi points to the experiences of two cruise ships. On one, which sailed in February when masking wasn’t common, 80 percent of the people infected onboard showed symptoms. On another, which sailed later in March when surgical masks were distributed to all passengers, fewer than 20 percent of infected people came down with symptoms.

How masks make a difference

Without more direct scientific studies, it’s still just a theory that masks can make COVID-19 infections less severe.

But scientists are getting a better understanding of how masks act as a defense. The virus can be sprayed around even by asymptomatic people through sneezing, coughing, singing, speaking or even breathing. Masks can create an effective barrier against these droplets, especially larger ones.

Certain coverings, like N95 respirators that should be reserved for health care professionals, are more effective than others. But even regular cloth masks can block up to 80 percent of viral particles.

“Everyone should wear a mask,” said Dean Blumberg, chief of pediatric infectious diseases at UC Davis Children’s Hospital, in an article from UC Davis. “People who say, ‘I don’t believe masks work,’ are ignoring scientific evidence. It’s not a belief system. It’s like saying, ‘I don’t believe in gravity.’”

Masks alone can’t completely block the spread of all virus particles, particularly smaller ones that can be 1/100th the size of a human hair. That’s why physical distancing and frequent hand washing are still critical. But shielding our faces is a simpler, more sustainable step than returning to community lockdowns, according to Dr. Gandhi.

Slowing the spread, one mask at a time

Now that masks have been mandated in different parts of the country, have they been effective at slowing the spread? The answer seems to be yes.

A study in Health Affairs found mandates to wear masks in 15 states and Washington, D.C, helped avert as many as 230,000–450,000 cases between April 8 and May 22, though the researchers cautioned that this was merely an approximation.

These findings have been supported by research around the world. A study in Germany found that local and regional mask mandates reduced “the daily growth rate of reported infections by around 40 percent.” And research out of China reported that households in which people used masks before the first person to get infected showed symptoms were “79 percent effective in reducing transmission.”

Like with most things in this pandemic, the scientific community is still learning more about mask-wearing every day. As it turns out, wearing one isn’t simply about protecting others – it looks like it can protect you too.