The following, written in an early phase of the COVID-19 pandemic in the U.S., is based on guidance from the American Medical Association at the time. Since then, masks have come to be seen as a useful, if imperfect, form of protection, and they have become more widely available.

If you've been thinking of buying a face mask to protect yourself from becoming infected with the COVID-19 virus, think again. Medical masks are designed to prevent the spread of respiratory infections. They work by covering the mouth and nose of the wearer. Because the coronavirus, COVID-19, affects the lungs, JAMA, The Journal of the American Medical Association, has published a Patient Page to let people know what masks can and cannot do, who should wear them and why they are unnecessary for most of us.

There are two types of masks that are being widely considered as protection, surgical face masks and what are called N95 respirators. Face masks tend to fit loosely. They prevent a person from spreading large sprays and droplets, as well as preventing hand-to-face contact. N95 respirators fit closer to the face and block 95 percent of airborne particles. They are commonly used when a person has tuberculosis, chickenpox and measles.

When not worn properly or worn at the wrong time, a mask may not only be ineffective, but can cause unintended ill effects.

People with moustaches and beards and children cannot use N95 respirators because it is difficult to achieve a proper fit.

When not worn properly or worn at the wrong time, a mask may not only be ineffective, but can cause unintended ill effects — by providing a false sense of security and making the wearer feel it's safe to touch his or her face or mouth. If this happens after exposure to a virus, it means a person could infect him or herself with the very virus he or she seeks to avoid.

Masks are designed to help the sick, not the well. Patients who have already contracted the virus do need to wear masks and have them readily available to prevent the spread of the virus they carry. When people who are simply worried about contracting the virus run out to buy a mask, the JAMA Patient Page points out, they may be reducing the access of healthcare professionals who need them when treating ill patients.

“The surgical masks really offer more protection for others than they do for the subjects that are wearing them. [However] people who actually have respiratory infections — if they are going to be in public places — should wear a mask,” infectious disease expert, Michael S. Simberkoff, M.D., told TheDoctor.

When Simberkoff, Professor of Medicine at New York University School of Medicine, and his colleagues looked at whether the use of N95 respirators or medical masks were more effective in preventing influenza infection among health care personnel in close contact with patients in a 2019 study, they found no significant difference in the level of protection offered by either type of mask.

People should stay at home when they are sick rather than use public transportation and infect others, advises Simberkoff. “If they have to travel to see a doctor at an emergency room, call ahead and let them know you have a respiratory illness. That is the time to wear a surgical mask.”

If you are among those who do need to wear a mask, wash your hands before putting it on, and place the face mask over your nose and mouth. Get a tight seal; make sure there are no gaps between the face mask and your face. Try to avoid touching the face mask when you are wearing it. If you do touch your face mask, wash your hands or use hand sanitizer again. When you take the mask off, avoid touching the front of it, and discard it in a closed bin. Wash your hands again.

Washing your hands often and for at least 20 seconds, including under the nails, is the best first line of defense against COVID-19. Unless instructed to buy them by your healthcare provider, you should resist the impulse to buy a mask. That will help make sure masks are available for healthcare workers and those who are ill.