What are the best masks against covid-19 and when to use them?

(CNN) -- Think of face masks as the newest fashion accessory that can save your life and the lives of your loved ones.

But instead of the pattern, logo, or slogan it displays, choose your mask based on its effectiveness against the deadly coronavirus in the environment you're in.

Guidelines on how to help you make that decision should be released in mid-spring, according to Jonathan Szalajda, deputy director of the National Laboratory for Personal Protection, which is part of the National Institute for Occupational Safety and Health at the Centers for Disease Control and Prevention. US Diseases (CDC).

Working closely with government agencies, industry stakeholders, and ASTM International, an international technical standards organization, the standards will apply to filter efficiency, size and fit, cleanliness, 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 say about how best to use them.

N95 type masks

Made from fibers woven with an electrical charge that can trap stray particles, like a sock sticking to your pants in the dryer, studies have shown that N95-type respirators are currently 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 if all Americans wore an N95-type mask for four weeks in risky environments 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.

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N95 respirators come in many sizes to fit various face shapes. When fitted to the wearer's face and worn correctly, 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 microns in diameter, or about 4 millionths of an inch.

While it may seem like N95 filters would miss the tiny covid particles, this is not the case. Most virus fragments leave the lungs encased within larger respiratory droplets, usually much larger than 0.3 microns.

Even those that are aerosolized are easily captured. Due to a natural phenomenon called Brownian motion, these tiny particles do not travel in a straight line. Instead, they bounce around in a zigzag fashion and easily get caught on the N95's electrostatic filter.

While some experts are calling for a nationwide rollout of N95 masks, these masks are currently reserved for healthcare professionals on the front lines of caring for COVID-19 patients. This is partly due to the scarcity of such masks, which are designed to be used once and thrown away, but also due to the training required to fit and wear the mask correctly.

"In a healthcare setting, there is an advantage because there is a degree of sophisticated training to educate people on how to properly use respirators that 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% effectiveness level: N99, N100, R95, R99, R100, P95, P99, and P100 masks. Some of these devices, which may resemble gas masks, have been granted emergency use authorization and can be used in non-surgical settings during the N95 mask shortage.

The N95 mask, and its sisters and brothers, better fit a person's unique facial contours on a bare face to maintain a watertight seal. So the mask must be worn correctly, even though such a high filtration can make breathing difficult. N95-type masks have a much higher breathing resistance than simple cloth or surgical masks.

"I've seen people with full beards wear the N95, or wear the 95 backwards, or just have it over their mouth and not over their nose and mouth because it's easier to breathe when you're not covering your nose," he said. Szalajda.

Note: Be careful with N95 masks with exhalation valves, as those valves return airflow to the environment. Also beware of counterfeit N95s sold online and in some commercial stores.

The CDC's National Institute for Occupational Safety and Health (NIOSH) lists dozens of counterfeit masks being sold as N95 or NIOSH-approved masks on its website, and offers the following tips on how to make sure you don't buy a fraudulent product:

Europe FFP2

In response to the spread of new and more contagious variants of covid-19, some European countries are requiring the use of FFP1 and FFP2 masks, which stand for "filtering facepiece respirator."

Note: The "P" means that the mask is very oil resistant and can be used to protect against non-oily and oily aerosols. By comparison, the "N" in N95 means that the mask is not oil resistant and cannot 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 an FFP3 is 99% effective against airborne infectious diseases.

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

France is also requiring citizens to leave homemade masks behind. Single-use FFP1 surgical masks and more protective FFP2 filtering facepiece respirators are now required in all public places.

France is also allowing people to wear commercial cloth 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 purchasing such masks.

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KN95 and similar filtering facepiece respirators

KN95 masks, which are certified to Chinese standards, also filter and capture 95% of 0.3 micron particles. But there are differences: The filter layers of N95 respirators were "8 times thicker and had 2 times the dipole charge density of KN95 respirators," according to a study published in December.

These KN95 masks are not NIOSH certified, but some manufacturers of KN95 masks have received emergency use approval for use in healthcare settings in the US.

The 3M company, which manufactures many filtering facepiece respirators, published a paper comparing N95 and European FFP2 respirators to the Chinese KN95, Australian-New Zealand P2, Korean First Class and Japanese DS2 and found that they were all "similar " regarding "filtering of non-oily particles, such as those resulting from wildfires, PM 2.5 from air pollution, volcanic eruptions, or bioaerosols (eg, viruses)."

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

Surgical grade masks

Designed for use by surgeons and other healthcare professionals, surgical-grade masks are loose-fitting, disposable devices intended to "help block large-particle droplets, aerosols, or splashes that may contain germs (viruses and bacteria), preventing them from reach the mouth and nose," according to the U.S. Food and Drug Administration (FDA).

They do not "filter or block very small airborne particles that can be spread by coughing, sneezing, or certain medical procedures," the FDA stressed.

"Surgical masks were not designed to perform respirator functions," said NPPTL's Szalajda. "They are not intended to protect against inhalation particles, but rather against contact with body fluids."

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

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

Surgical masks are single-use, and if they are dirty or breathing becomes difficult, the mask should be carefully discarded and replaced, the FDA said.

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Homemade cloth masks

The most commonly used mask among the general public today is a cloth mask, often made at home. The effectiveness depends on the type of fabric used and the number of layers of fabric. These masks can be as little as 26% effective.

According to the CDC, "Multiple layers of higher thread count fabric have shown superior performance compared to single layers of lower thread count fabric, in some cases filtering nearly 50% of fine particles smaller 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 wick away moisture when used in masks or as mask inserts.

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

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

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

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

President Joe Biden has been seen wearing two masks on numerous occasions. On the day of the inauguration, Transportation Secretary candidate Pete Buttigieg and his husband, Chasten Glezman, took a double-masked selfie and inaugural poet Amanda Gorman wore a surgical mask under her version. from prada.

It's a behavior advocated by Joseph Allen, an associate professor at the Harvard TH Chan School of Public Health and director of the school's Healthy Buildings program.

"A surgical mask with a cloth mask on top can achieve greater than 91% particle removal efficiency," Allen recently told Dr. Gupta's team.

Double-masking makes sense, according to Dr. Anthony Fauci, now chief medical adviser to Biden.

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"If you have a physical cover with one layer, you put on another layer, it just makes common sense that it's probably more effective and that's why you see people doing double skins or doing a version of an N95," he told her. Fauci to NBC's Savannah Guthrie.

But be careful about putting on any mask, Allen told CNN last fall. "You want the mask to go over the bridge of the nose, under the chin, and sit flush with the face, resting along the skin."

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Face shields, bandanas, gaiters, balaclavas, and scarves

Certain items do not provide a sufficient barrier against COVID-19 and other viruses and should not be used as a means of meaningful protection, according to the CDC.

Don't wear knitted scarves or balaclavas as a protective measure, the CDC says. Don't wear a face shield without a mask, the agency warns, as it won't protect against small airborne droplets that can float under and into the shield. And forget about bandanas and leggings.

A 2020 study from Duke University examined 14 commonly available face coverings. As expected, the tight-fitting N95 was considered most effective, followed by three-layer surgical masks. But the study found that folded bandannas, knitted masks and neck scarves didn't offer much protection at all.

In fact, gaiter masks, also known as neck fleeces, actually increased respiratory droplet transmission.

CNN's Keri Enriquez and Eliza Mackintosh contributed to this story.

Editor's Note: This note was originally published in January 2021 and was updated in July 2021.