People with chronic health conditions, especially those with compromised immune systems, were some of the earliest adopters of face masks when the COVID-19 pandemic struck. They wore them even before it was encouraged by health officials. Now that many states have mandated their use, face masks are ubiquitous.

Ed Tessaro, a patient advocate for the Muscular Dystrophy Association (MDA), appreciates the push for mask wearing. The 73-year-old from Atlanta was diagnosed with familial amyotrophic lateral sclerosis (ALS), a degenerative disease that leads to loss of muscle control and progresses much more slowly than nonfamilial ALS, in 2009. (MDA is an umbrella organization for neuromuscular diseases like ALS.) In his advocate role and his personal life, he urges people to take masks seriously.

Public health officials initially discouraged people from wearing masks in part out of fear there wouldn't be enough for hospital workers, but they began urging Americans to cover their faces once supplies became more plentiful and studies made it clear how masks could prevent transmission.

The change in recommendations didn't surprise Richard Besser, MD, a former acting director of the US Centers for Disease Control and Prevention (CDC) and now president and CEO of the Robert Wood Johnson Foundation in New Brunswick, NJ, which funds public health initiatives. "We've been learning a lot over the course of this pandemic," he says. "We're trying to understand how masks can be most effective."

The CDC updated its guidance on masks after cases spiked in the spring and it discovered that COVID-19 can be spread by people who are infected but asymptomatic. "Studies have found that viral load peaks in the days before symptoms begin and that speaking is enough to expel virus-carrying droplets," says Peter Chin-Hong, MD, professor of medicine at the University of California San Francisco, who specializes in treating infectious diseases.

An experiment using high-speed video, described in a research letter in the April 15, 2020, issue of the New England Journal of Medicine, showed that of the hundreds of droplets generated when a person speaks a simple phrase, nearly all were blocked if the person's mouth was covered by a damp washcloth.

Other research, reported in June in Health Affairs, compared the rate of new COVID-19 cases before and after mask requirements in 15 states and the District of Columbia: The daily growth rate of COVID-19 cases slowed by less than one percentage point in the first five days of a mandate and by two percentage points after three weeks.

Several publicized incidents have also supported the importance of masks in preventing transmission. In one case, a man tested positive for COVID-19 after he flew from China to Toronto in January. Yet all 25 people nearest him on the flight—during which he had a dry cough and wore a mask-tested negative for the virus. In late May, two hairstylists in Missouri had close contact with 140 clients while sick with COVID-19; everyone had been wearing masks, and none of the clients tested positive.

While doctors agree that masks are most useful when worn by someone with the virus, a mask also reduces the amount of virus that a wearer takes in—which could lessen the severity of an illness if that person subsequently develops COVID-19—according to a study in the July issue of the Journal of General Internal Medicine.

Still, wearing a mask is just one protective measure people should take. "In general, masks are not a substitute for good social distancing, hand hygiene, and for staying home if you are sick," says B. Scott Segal, MD, chair of anesthesiology at Wake Forest Baptist Medical Center in Winston-Salem, NC, who has conducted studies on consumer masks.

As face coverings are now a reality of everyday life, it makes sense to become familiar with each type of mask.

N95

This mask, which is worn by health care workers and must meet federal manufacturing standards, is so named because it's designed to block 95 percent of small particles, including bacteria and viruses. Meant to fit snugly to the face, it is fastened by elastic bands around the back of the head. "These medical devices prevent exposure to tiny droplets that can remain suspended in the air. Health care workers undergo a fit test to find the right make, model, and size to ensure a tight seal," says William Schaffner, MD, medical director of the National Foundation for Infectious Diseases and a professor of medicine at the Vanderbilt University School of Medicine in Nashville. N95 masks should be reserved for medical workers because they are in short supply and because the required tight fit makes it likely that nonmedical personnel will not wear them correctly and thus may expel more virus wearing them, says Dr. Schaffner. Authentic KN95 masks, which are manufactured in China, are as effective as N95 masks.

Procedure/Surgical

These disposable, usually light blue masks look similar to each other, but surgical masks are tied behind the head with strings while procedure masks have elastic straps that fit over the ears. Both masks are made of three layers, usually a combination of plastic and paper, and have a nose piece to hold the mask in place. Neither type seals like N95 masks, so surgical and procedure masks provide less protection from airborne pathogens, but they do filter out large particles and prevent the wearer's droplets from spreading. Surgical masks are worn during surgery, procedure masks during other procedures. The surgical kind may fit the face and filter out particles better, says Dr. Segal. The US Food and Drug Administration has not approved any specific type of disposable mask for protection against the coronavirus.

Cloth

Tightness of the weave is crucial when it comes to cloth masks, experts say; the outline of individual fibers shouldn't be visible when the material is held up to light. "In our testing, the best-filtering masks were made of two layers of high-quality 'quilting' cotton," says Dr. Segal. "A layer of cotton with a flannel inner layer also did very well." Dr. Segal says none of the fabric masks his team tested performed as well as surgical or procedure masks on the smallest microscopic particles (0.3 microns, or thousandths of a millimeter), but they did on slightly larger but still microscopic particles (one to two microns). Laundering a cloth mask, which may tighten the weave, may slightly improve its effectiveness for the smallest particles, says Dr. Segal. The mask should cover the nose, mouth, and chin with no gaps and stay put when the wearer is talking. Masks with a bendable metal nose strip may create a tighter seal, hold the mask in place better, and prevent glasses from fogging up.

Filters

Adding a filter, such as a blue shop towel—a heavy-duty paper towel that doesn't block all airflow as some paper towels do—to a lower-quality mask may increase its effectiveness, says Dr. Segal. "Air-conditioning filters seem quite effective with low resistance to breathing, so those and the towels performed the best in our tests," he says. "Coffee filters absorb liquid, but they weren't great in our tests. We didn't test facial tissues, but other researchers have and claim they were quite effective. I don't think they'd last long if they got even a little wet."

Others

A study published in Science Advances in August found that stretch "gaiters," which go over the head and pull up from the neck to the nose, are not sufficiently protective. And the CDC has advised against wearing masks with airflow vents or valves because air expelled through these holes allows respiratory droplets to reach others. "Valves make masks more comfortable," says Dr. Segal, "but they defeat the public health rationale for having everyone wear them: to protect others from you if you are infected and don't know it."

How to Protect Yourself if Wearing a Mask Is Challenging

Some people are too claustrophobic to wear a mask or are overly sensitive to having fabric touch their face. Many neurologic disorders can cause sensory problems, including cerebral palsy, autism, attention deficit hyperactivity disorder, fragile X syndrome, and sensory processing disorder, says Shifra K. Leiser, occupational therapist (OT) and assistant professor in the occupational therapy program at Touro College in New York City. In those situations, she suggests choosing masks with soft and unscented fabric, which may lessen the discomfort. “There is a growing array of sensory-friendly, protective masks on the market made from a variety of materials and with alternate methods of attachment,” Leiser says. “Finding a comfortable material, avoiding the pull of elastic behind the ears, providing a better fit, or selecting a preferred color or pattern may make it easier to wear a mask.” She also recommends working with an OT on desensitization exercises such as tapping and massaging along various nerve pathways while monitoring for response and effectiveness.

People with epilepsy may worry that a mask will make them hyperventilate and have a seizure. Those who feel they cannot wear a mask must be hypervigilant about social distancing, handwashing, and avoiding potentially risky situations, says James J. Sejvar, MD, a neurologist and epidemiologist at the US Centers for Disease Control and Prevention. “Limit your activity rather than your mask wearing,” he says. For example, if you cannot wear a mask in a grocery store, ask someone to shop for you.

Or consider donning a plastic face shield, which may protect others from sneezes and coughs, although not as effectively as cloth and surgical masks, says Dr. Sejvar. A shield is an alternative if sensory stimulation is a problem, and it can help you feel safer when walking outside or doing other socially distanced activities.

If you can wear a mask but think it impedes communication during doctor’s appointments—by muffling sounds and hiding facial expressions—Dr. Sejvar suggests asking the doctor and his or her staff to speak louder, write down important information to share with you, and follow up with an email about what was discussed. If you feel claustrophobic, remove your mask briefly while turning your head away from other people, Dr. Sejvar says.

John Kindschuh, 37, who still has residual effects of a stroke several years ago, says he feels unstable if he has to put on a mask quickly. “I have learned to stop walking and sit down, so I can fasten it properly and securely without covering my eyes.” Kindschuh, who lives in St. Louis, doesn’t object to the inconvenience, given the possible alternative: “I almost died from my stroke, so I choose to avoid a second life-threatening situation.”