The type and quality of the mask matters, too. A CDC study released Friday found that people who consistently wear a high-quality mask, such as an N95 or KN95, in an indoor public setting appear to have the best chance of avoiding Covid. The CDC report looked at randomly selected California residents who had received either a negative or positive Covid test between Feb. 18 and Dec. 1.

It found that when someone wore a cloth mask, the odds of testing positive for Covid infection were reduced by 56 percent. A surgical mask lowered the odds by 66 percent. People who wore an N95 or KN95 were 83 percent less likely to test positive for Covid.

The report came weeks after the agency updated its guidance on masks for the general public, saying people “may choose” to wear N95 and KN95 masks because they offer the best protection against this virus.

An N95-caliber mask can “provide you with as optimal protection as possible irrespective of what those around you are doing,” said Ranu Dhillon, an epidemic response specialist at Harvard Medical School.