WASHINGTON - Experts seem to agree: If you are not a health care worker, do not buy N95 masks, long considered the Cadillac of protective masks.
They will not help you much, and they are in extremely short supply for the people who need them most: front-line health care workers trying to protect themselves from COVID-19 while they save lives.
That said, there is still debate over whether everyone should wear some kind of face covering when they go outside.
Staying home and limiting contact with groups of people remains the best way to stop the pandemic.
But some experts are starting to suggest that some kind of face covering may help, not by protecting the wearer from infection, but by protecting others from the wearer.
There's growing evidence that people can spread the disease without having symptoms themselves, though it's not the biggest factor driving the pandemic. Two studies have linked 6 percent to 13 percent of infections to people who weren't showing symptoms.
Masks "may help protect people who are infectious from transmitting (the disease)," said Harvard University epidemiology professor Bill Hanage. "And if there is a large proportion of people who are mostly asymptomatic, then they could have an outsized role."
The SARS-CoV-2 virus, which causes COVID-19, spreads mostly through droplets that infected people expel from their mouths. That happens when people cough or sneeze — which you should always do into your sleeve — but also when they talk or sing.
If virus-laden droplets land on surfaces, people can pick them up on their hands. From the hands, it's a short trip to the eyes, nose or mouth, and from there to infection.
Masks may help by blocking at least some of those droplets.
"I don't think it's going to be the most effective tool in our toolbox, but I think it might help," said Tim Schacker, vice dean for research at the University of Minnesota Medical School.
However, he added, "this is a tough question because like all things COVID, we lack data."
There's not much definitive research on how well face masks of any kind work to prevent any disease, and even less for brand-new COVID-19.
N95 masks generally are best for preventing someone from catching the virus because, when used properly, they fit tightly across the face and block the most particles.
However, many people don't use them properly. They often don't get a tight fit, which largely defeats the purpose.
Dr. Chongfei Jin, a staff physician at Patient First in Alexandria and Gainesville, Virginia, said that when talking to patients, he always corrected how they were wearing their masks. He said there are many videos available online that show how to wear the mask correctly.
“I just want to remind the public three things: Avoid inside out. Avoid upside down. And cover your nose as well,” he said.
Health care workers are facing serious shortages in part because the panicked public has cleared the shelves.
"If they run out of masks, then it's very difficult for them to stay healthy to take care of you and me when we get sick," said George Washington University global health professor Jon Andrus.
Also, "we know the people who wear masks tend to touch their faces more," Harvard's Bill Hanage said, "and given that touching your face is a potential route of transmission, we would have to figure out" whether the benefits outweighs the risks.
Surgical masks are another popular choice. But experts say they provide limited protection from the coronavirus since they do not fit tightly. They may help prevent you from infecting others, but health workers should get first priority.
The same goes for fabric masks. But it's not clear how much protection different kinds of fabric provide.
Some efforts have aimed to enlist the public to sew fabric masks for health care workers facing extreme shortages.
These masks don't provide the usual level of protection.
"A homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals," concluded one study, "but it would be better than no protection."
Jin, the Virginia doctor, said a “homemade mask, I believe that is the last resort. If you have a surgical mask, please use the surgical mask [as] that's much better. But if you don't, the homemade mask” can be helpful in protecting the wearer from virus-laden droplets.
And those masks could themselves spread disease if they aren't handled properly.
"My mother used to wash our clothes after we went backpacking," Andrus said. "She always got poison oak [an itchy rash caused by oil from a plant] but never went backpacking with us."
Andrus is worried that masks will give wearers a false sense of security. It's no substitute for social distancing, he said.
But, "This is a war," he said. "Anything we can do to minimize risk is critically important."