Chinese authorities have encouraged people in the city of Wuhan to wear surgical masks in public to help curb the spread of the new coronavirus.

The question is: do they work?

Many infectious disease specialists say the cheap disposable masks, which cover the nose and mouth, may help prevent the spread of infections if they are worn properly and used consistently.

But there isn’t much high-quality scientific evidence on their effectiveness outside health care settings, experts say. Most of the best studies, which are randomized controlled trials, focused on how well surgical masks protect health care workers in hospitals from picking up infections from sick patients, and found that consistent use of them helped.

Dr. Julie Vaishampayan, chairwoman of the public health committee for the Infectious Diseases Society of America, said surgical masks are really “the last line of defense.”