Coronavirus masks: Which mask is best for you, and when to use it

Think of masks as the newest trendy accessory that can save your life -- and the lives of those you love.

But instead of what pattern, logo or slogan you display, choose your mask based on its effectiveness against the deadly coronavirus in the environment you are in.

Guidelines on how to help you make that choice should be out by midspring, according to Jonathan Szalajda, deputy director at the National Personal Protective Technology Laboratory, which is part of the National Institute for Occupational Safety and Health at the US Centers for Disease Control and Prevention.

Working closely with government agencies, industry stakeholders and ASTM International, an international technical standards organization, the standards will apply to filter efficiency, sizing and fit, cleaning and recommended period of use or reuse.

For now, here's a breakdown of respirators and masks based on current scientific knowledge, and what experts are saying on how to best use them.

N95-type masks

Made from fibers woven with an electrical charge that can trap errant particles -- like a sock that sticks to your pants in the dryer -- studies have shown N95-type respirators are currently at the top of the line when it comes to filtering large and small particles. Masks in this category are also known as "filtering facepiece respirators" or "disposable respirators."

What would happen if every American wore an N95-type mask for four weeks in risky settings like being indoors?

"It would stop the epidemic," Dr. Abraar Karan, an internal medicine physician at Brigham and Women's Hospital and Harvard Medical School, told CNN Chief Medical Correspondent Dr. Sanjay Gupta.

N95 respirators come in many sizes to accommodate various face shapes. When fitted to the wearer's face and worn properly, N95-type masks can trap 95% of particles around 0.3 microns, studies have shown. SARS CoV-2 can be as small as 0.1 micron in diameter -- that's about 4 millionths of an inch.

While it may seem that N95 filters would miss the tiny Covid particles, that's not so. Most bits of virus exit the lungs encased inside larger respiratory droplets, typically much bigger than 0.3 microns.

Even those that become aerosolized are easily captured. Due to a natural phenomenon called Brownian motion, such minute particles don't travel in straight lines. Instead they bounce around in a zigzag fashion and are easily caught in the N95's electrostatic filter.

While some experts are calling for a nationwide rollout of N95 masks, such masks are currently reserved for health care professionals on the front lines of caring for Covid-19 patients. That's partly due to a shortage of such masks, which are designed to be worn once and discarded, but also due to the training needed to fit and wear the mask properly.

"In a health care setting, there's an advantage because there's a degree of sophisticated training to inform people how to properly wear respirators which doesn't exist in a public setting," NPPTL's Szalajda said.

According to the CDC, a few other respirators also meet or exceed the 95% efficacy level: the N99, N100, R95, R99, R100, P95, P99 and P100 masks. Some of these devices -- which can look like gas masks -- have received an emergency use authorization and can be used in nonsurgical settings during shortages of N95 masks.

The N95 mask -- and its sisters and brothers -- is best fitted to a person's unique facial contours on a bare face to keep the seal tight. Then the mask must be worn properly, despite the fact that such high filtration can make breathing more difficult. N95-type masks have a much higher breathing resistance than simple surgical or fabric masks.

"I've seen people with a full beard wearing the N95, or they're wearing the 95 upside down, or they just have it over their mouth and not their nose and mouth because it's easier to breathe when you're not covering your nose," Szalajda said.

Note: Beware of N95 masks with exhalation valves in them, since those valves put your airflow back into the environment. Also beware of knockoff N95s being sold on the internet and at some commercial stores.

The CDC's NIOSH lists dozens of counterfeit masks being sold as N95 or NIOSH-approved masks on its website, and offers the following advice on how to be sure you are not buying a fraudulent product:

• NIOSH-approved respirators carry an approval label on or within the packaging of the respirator and on the mask itself.
• NIOSH-approved respirators will always have one of the following designations: N95, N99, N100, R95, R99, R100, P95, P99 or P100.
• You can verify the approval number on the agency's equipment list or trusted-source page to determine if the respirator has been approved by NIOSH.

Europe's FFP2

In response to the spread of new, more contagious variants of the coronavirus, some European countries are mandating the use of FFP1 and FFP2 masks -- which stand for "filtering facepiece respirator."

• Note: The "P" means the mask is strongly resistant to oil and can be used to protect against nonoily and oily aerosols. In comparison, the "N" on N95 means the mask is not resistant to oil and can't be used in an oil droplet environment (such as drilling for oil).

An FFP1 filter has a minimum filtration efficiency of 80%, an FFP2 is 94% effective and a FFP3 is 99% effective against airborne infectious diseases.

Last week the German state of Bavaria mandated that citizens use FFP2 masks when shopping in stores and traveling on public transport. The German government then followed that lead, requiring everyone in the country to wear either FFP1 or FFP2 masks while at work, in shops or traveling on public transport.

France is also requiring citizens to leave homemade masks behind. Now single-use surgical FFP1 masks and more protective FFP2 filtering facepiece respirators are required in all public places. France is also allowing people to use commercial fabric masks certified to filter 90% of particles greater than or equal to 3 microns. Citizens are told to look for the "filtration guarantee" logo when buying such masks.

KN95 and similar filtering facepiece respirators

The KN95 masks, which are certified via Chinese standards, also filter out and capture 95% of 0.3 micron particles. But there are differences: Filter layers of N95 respirators were "8-fold thicker and had 2-fold higher dipole charge density than that of KN95 respirators," a study published in December found.

These KN95 masks are not certified by the US National Institute for Occupational Safety and Health, but a few manufacturers of KN95 masks have been given emergency use approval to be used in health care settings in the US.

The company 3M, which makes many filtering facepiece respirators, put out a document comparing N95 and European FFP2 respirators to the Chinese KN95, the Australia-New Zealand P2, the Korean 1st Class and the Japanese DS2 and found all of them "similar" in regard to "filtering non-oil-based particles such as those resulting from wildfires, PM (small particle) 2.5 air pollution, volcanic eruptions, or bioaerosols (e.g. viruses).

"However, prior to selecting a respirator," the 3M document said, "users should consult their local respiratory protection regulations and requirements or check with their local public health authorities for selection guidance."

Surgical-grade masks

Designed to be used by surgeons and other health care professionals, surgical-grade masks are loose-fitting, disposable devices meant to "help block large-particle droplets, splashes, sprays, or splatter that may contain germs (viruses and bacteria), keeping it from reaching your mouth and nose," according to the US Food and Drug Administration.

They do not "filter or block very small particles in the air that may be transmitted by coughs, sneezes, or certain medical procedures," the FDA stressed.

"Surgical masks weren't meant to perform the functions of the respirator," said NPPTL's Szalajda. "They're not intended to be protection from inhalation particles but from contact with body fluids."

True medical-grade masks are made of three layers of nonwoven fabric typically made from plastic. The colored top layer of fabric is made of medical-grade spunbond polypropylene, which is a resin polymer heat-bonded into a weblike structure.

Surgical masks also have small, bendable wires to help the mask stay in place, and are often tied behind the head or secured with ear ties. This design doesn't make for a particularly great fit, especially compared to the N95, according to Szalajda.

Surgical masks are one-time use only, and if they are soiled or breathing becomes difficult, the mask should be carefully discarded and replaced, the FDA said.

Homemade cloth masks

The most common mask in use among the general public today is a fabric mask, often homemade. Effectiveness depends on the type of fabric used and the number of layers of cloth. These masks can be as little as 26% effective.

According to the CDC, "multiple layers of cloth with higher thread counts have demonstrated superior performance compared to single layers of cloth with lower thread counts, in some cases filtering nearly 50% of fine particles less than 1 micron."

That's good news -- studies have detected SARS‐CoV‐2 in aerosols between 1 and 4 microns.

A study published last September examined the ability of cotton, polyester and silk to repeal moisture when used in masks or as mask inserts.

"We found that silk face coverings repelled droplets in spray tests as well as disposable single-use surgical masks," the authors wrote, adding that silk masks "can be more breathable than other fabrics that trap humidity, and are re-useable via cleaning."

Whatever the fabric, look for a tight weave, according to studies. Use the light test to check the weave: If you can easily see the outline of the individual fibers when you hold up the mask to the light, it's not likely to be effective.

You can also add filters to your fabric mask, according to the CDC. Some are made from polypropylene, the plastic that produces static cling; others from silver or copper, which have antimicrobial properties. Studies on the effectiveness of inserts, however, are rare, so guidance is limited.

To up their odds, people have begun layering fabric masks over surgical ones for added protection.

President Joseph R. Biden has been seen wearing two masks on numerous occasions. On Inauguration Day, Transportation Secretary nominee Pete Buttigieg and his husband, Chasten Glezman, took a selfie double-masking and inaugural poet Amanda Gorman wore a surgical mask beneath her Prada version.

It's a behavior advocated by Joseph Allen, an associate professor at the Harvard T.H. Chan School of Public Health and the director of the school's Healthy Buildings program.

"A surgical mask with a cloth mask on top of it can get you over 91% removal efficiency for particles," Allen recently told Dr. Gupta's team.

It makes good sense to double mask, according to Dr. Anthony Fauci, now chief medical adviser to Biden.

"If you have a physical covering with one layer, you put another layer on, it just makes common sense that it likely would be more effective and that's the reason why you see people either double masking or doing a version of an N95." Fauci told NBC's Savannah Guthrie.

But pay attention to fit on any mask, Allen told CNN last fall. "You want the mask to go over the bridge of the nose, below the chin and be flush on the face, resting along the skin."

Face shields, bandanas, gaiters, ski masks and scarves

Certain items fail to provide a sufficient barrier against Covid-19 and other viruses and should not be worn as a means of significant protection, according to the CDC.

Don't wear scarfs or knitted ski masks as a protective measure, the CDC says. Do not wear a face shield without a mask, the agency advises, as it won't protect against tiny airborne droplets that can float under and inside the shield. And forget bandanas and neck gaiters.

A 2020 study by Duke University looked at 14 commonly available face coverings. Not surprisingly, the fitted N95 was judged most effective, followed by three-layer surgical masks. But the study found folded bandanas, knitted masks and neck gaiters did not offer much protection at all.

In fact, gaiter masks, also known as neck fleeces, actually increased the transmission of respiratory droplets.