Experts seem to agree: If you are not a health care worker, do not buy N95 masks, long considered the best of protective masks.
They will not help you much, and they are in extremely short supply for the people who need them most: health care workers trying to protect themselves from COVID-19 while saving lives.
However, there is still debate over whether everyone should wear some kind of face covering when they leave their homes.
Staying home and limiting contact with groups of people remain the best ways to stop the spread of the new coronavirus.
But some experts suggest that some kind of face covering may help, too -- not by protecting the wearer from infection, but by protecting others from the wearer.
There is growing evidence that people can spread the disease without having signs of sickness themselves. Two studies have linked 6 percent to 13 percent of infections to people who were not showing any signs of infections themselves.
The new coronavirus, which causes COVID-19, spreads mostly through small drops of liquid that infected people expel from their mouths. That happens when they cough or sneeze. But it can also happen when they talk or sing.
If virus-infected drops of liquid land on surfaces, people who touch the surface get the drops on their hands. From the hands, it is a short trip to the eyes, nose or mouth. 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. He is 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 is not much definitive research on how well face masks of any kind work to prevent any disease, and even less research for a new disease like COVID-19.
N95 masks generally are best for preventing someone from catching a virus. When used correctly, they fit closely onto the face and block more particles than most other masks.
However, many people do not use them correctly. They often do not get a tight enough fit, which largely defeats the purpose of the masks.
Dr. Chongfei Jin works at Patient First in the state of Virginia. He said there are many videos available online that show how to wear the mask the right way.
He said, "I just want to remind the public three things: Avoid inside out. Avoid upside down. And cover your nose as well."
Health care workers are facing serious shortages in part because the panicked public has bought N95 masks for themselves.
"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 Jon Andrus, a professor of global health at George Washington University in Washington, D.C.
Surgical masks are another popular choice. But experts say they provide limited protection from the coronavirus since they do not fit as closely to the face. They may help prevent the wearer from infecting others. But again, the masks should be saved for health care workers.
Some cloth masks may also help protect the public too. But it is not clear how much protection different kinds of fabric provide.
Some efforts have aimed to ask the public to sew fabric masks for health care workers facing extreme shortages. But, these homemade masks do not provide the usual level of protection.
One study from 2020 states, "A homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals." The researchers added, "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."
Andrus, the global health professor, is worried that masks will give wearers a false sense of security. Wearing a mask of any kind is no substitute for social distancing, he said.
But, "This is a war," he added. "Anything we can do to minimize risk is critically important."