A lot of the effort to slow the spread of the coronavirus comes down to a seemingly simple concept: Wearing a mask.
But the issue has proven a thorny one. Health authorities have changed their guidance on who should wear masks and when to wear them. This has led to some confusion and even suspicion.
But since the coronavirus first appeared, authorities have gained a better understanding of how it spreads and how masks can help stop that spread.
Here's a look at how what we know about masks has changed, and how government officials are increasingly getting behind the idea of mandating the use of masks.
WHAT DO THE EXPERTS SAY?
The U.S. Centers for Disease Control and Prevention has long advised people to wear masks because they help prevent people who are infected — whether they know it or not — from spreading the coronavirus.
But last week, the CDC added a new reason: masks can also protect wearers who are not infected, though to a lesser degree.
The agency referred to a study led by Japanese researchers that found masks block about 60% of the amount of virus that comes out of an infected person. When an uninfected person wearing a mask is near an infected person who isn't wearing one, the amount of virus the uninfected person inhaled fell by up to 50%.