Our Members Asked:
Which is the best mask to prevent COVID-19 and how do cloth, disposable, N95, and KN95 masks compare? How can I stop glasses from fogging?
Although N95 masks are the gold standard and were, until the spring of 2020, easily obtainable, good mask options exist, primarily certified KN95 masks and well-made, well-fitting, 3-layer cloth masks. Disposable surgical masks are also readily available but tend to leave gaps between the mask and face, reducing their usefulness. Electrical air purifying respirators that mimic powered air-purifying respirators (PAPRs) exist, but these devices would not be appropriate for preventing the spread of COVID-19 among the general public.
If you want to find and buy a good mask that meets the guidelines of the U.S. CDC as well as the World Health Organization, go right to the Best Cloth Masks You Can Buy
If you want a KN95 respirator, see the Finding the Best KN95 Masks section.
If you want to make your own mask (which can be quite effective) see the Best combination of materials for making a mask section. We also identify what seem to be the best disposable filter materials.
Masks can be used alone or, for increased protection, particularly for the eyes, with a face shield — which we have also reviewed.
Here's what we cover in this answer:
- Why You Should Wear a Mask -- and Why It Should Be an Efficient One
- Best Combination of Materials For a Mask
- How Cotton and Other Household Fabrics Compare in Blocking Coronavirus
- Best Materials for Mask Filters
- Best Cloth Masks
- Best KN95 (Respirator) Masks
- Best Disposable Surgical/Medical Masks
- Other Types of Masks and Respirators
- Cleaning and Caring for Masks
- How to Improve Mask Fit to Reduce Leakage
- How to Reduce Eyeglass Fogging
- Concerns About Co2 Build Up
- Concern with Inhaling Microplastics
- Are Copper Masks Better?
- What Masks Protect Against Wildfire Smoke?
Why you should wear a mask -- and why it should be an efficient one
Along with social distancing, a mask provides additional protection from infecting others as well as preventing exposure. In addition, according to the CDC, "cloth mask materials can also reduce wearers' exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns." A review of studies found that transmission of SARS-CoV-2 and related coronaviruses was 82% lower with physical distancing of 1 meter (3.3 feet) or more, compared with shorter distances, and protection might increase with additional distance. Face mask use could result in an 85% reduction in risk of infection versus no face mask, with stronger associations for N-95 or similar respirators, while surgical masks and multi-layered cotton masks were less effective but offered more protection than single-layer masks (Chu, Lancet 2020).
An analysis of rates of growth of COVID-19 infection in U.S. states found that the mandated use of masks in public issued by 15 states in April and May, 2020 was associated with a decline of about 1% in the daily COVID-19 growth rate within the first week of the mandates and a 2% decline 21+ days after mandates were issued. Although the effect is modest, the researchers estimated that by May 22, 2020, 230,000 to 450,000 COVID-19 cases may have been averted due to the mandates (Lyu, Health Aff 2020).
As wearing a mask may reduce the amount of virus to which a wearer is exposed, it has been postulated that even if a mask-wearing person becomes infected, the reduced viral load to which they were exposed may mean that they suffer a milder disease. Supporting this theory is a study that showed that hamsters protected with a surgical mask partition were less likely to become infected with SARS-CoV-2 than those without the partition, and those that did get sick had milder illness. In addition, on cruise ships with COVID-19 outbreaks, the majority of infected patients (81%) were asymptomatic on a ship that had provided masks to all passengers and staff compared to only 18% of cases being asymptomatic on a cruise ship without masking (Gandhi, J Gen Intern Med 2020; Gandhi, N Engl J Med 2020).
Another benefit of wearing a mask is that, due to the heat and moisture of exhaled breath, masks have been shown to increase the humidity and temperature of inhaled air, which, researchers have proposed, may reduce the risk of respiratory infections such as COVID by promoting the clearance of pathogens in the lungs (Courtney, Biophysical J 2021 -- preprint).
When Do You Have to Wear a Mask?
As of February 1, 2021 masks must be worn by passengers on all forms of public transportation (e.g., airplanes, ships, ferries, trains, subways, buses, taxis, ride-shares) traveling into, within, or out of the U.S. (CDC January 29, 2021). Masks are also required while awaiting, boarding, and disembarking from public transportation. Transportation operators, such as crew, drivers, conductors, etc. are also required to wear masks. Masks can be bought or homemade, reusable or disposable, but must fully cover the nose and mouth. Clear panel masks are acceptable to facilitate communication with people who are hearing impaired or who otherwise need to see a speaker's mouth in order to communicate. Medical masks and N95 respirators are also acceptable. In addition to fully covering the nose and mouth, masks should also fulfill the following guidelines:
- Cloth masks should be made with two or more layers of a breathable fabric that is tightly woven (i.e., fabrics that do not let light pass through when held up to a light source). (See our Top Picks among cloth masks that meet these requirements.) If gaiters are worn, they should have two layers of fabric or be folded to make two layers.
- Masks should fit snugly but comfortably against the side of the face.
- Masks should be a solid piece of material without slits, exhalation valves, or punctures.
Face shields and goggles can be worn with masks, but cannot be worn instead of a mask. (See our Top Pick among face shields).
Failure to wear a mask as described above is a violation of federal law and can be enforced by the Transportation Security Administration (TSA) and state and local authorities. The TSA has proposed a fine of $250 for the first offense up to $1,500 for repeat offenders (TSA 2021). However, there are several exceptions to the requirement: Masks may be removed for brief periods of time when eating, drinking, or taking medication, while communicating with someone who is hearing impaired, when required to verify one's identity, and when requested by a ticket agent or law enforcement officer.
Governments in several European countries have gone a step further, and, in January, mandated the use of masks or respirators documented to provide at least 80 to 95% filtration efficiency in public areas, particularly on public transport and in shops. Respirators in Europe are referred to as filtering facepieces, or FFPs, and are classified as FFP2 (filtering ≥94% of aerosols, total inward leakage <8%) or FFP1 (filtering ≥80% of aerosols, total inward leakage <22%). Austria has the most stringent requirement, requiring FFP2 masks, which provide similar levels of filtration as N95 and KN95 masks. (See our Top Picks among KN95 masks).
Any benefit to wearing masks at home?
Although CDC guidelines do not currently include the use of face masks at home, the rate of transmission from one household family member to another was 79% lower when members wore face masks prior to the first member developing COVID-19 symptoms, according to a study of 124 families in Beijing in which there was at least one infected person. Overall, there was a 23% rate of transmission of COVID-19 from an infected family member to another, but this was no lower when mask wearing began after the first member developed symptoms. These results are consistent with the fact that viral load is highest two days before symptoms and on the first day of symptoms. Daily use of disinfectants reduced transmission by 77%. Transmission rates were four times higher if the primary case had diarrhea and 18 times higher when there was frequent daily close contact (less than 3 feet apart). The researchers recommended use of face masks in families in which a member has been at risk of getting infected. In China, over 70% of transmission occurred within families (Wang, BMJ Global Health 2020).
Best combination of materials for making a mask
Currently, both the CDC and WHO provide basic guidelines for choosing a cloth mask.
According to CDC guidelines, a cloth mask should:
- Use a minimum of 2 - 3 layers, preferably with batting between the layers
- Use fabrics with high thread count and fine weave, water-resistant fabric, and hybrid fabrics such as cotton-silk, cotton-chiffon, or cotton-flannel (cotton blends may be better than pure cotton). (In addition, the CDC notes that, due to their electrostatic charge, materials such as polypropylene may enhance filtration efficacy and fabrics such as silk can help to repel droplets.)
- Cover the nose and chin
- Fit snugly on the sides of the face without gaps
- Be secured with ties or ear loops
- Use ties rather than ear loops because ties provide better fit
- Made of fabric that makes it hard to breathe, such as vinyl
- Have exhalation valves or vents, as this allows virus particles to escape
- Intended for healthcare workers, such as N95s and surgical masks
1. Innermost layer: Hydrophilic material (i.e., one that can absorb moisture, such as cotton or cotton blends)
2. Middle layer: Hydrophobic material (i.e., repels moisture) of synthetic non-woven material such as polypropylene or a second cotton layer which may enhance filtration or retain droplets.
3. Outermost layer: Hydrophobic material (e.g., polypropylene, polyester, or their blends) which may limit external contamination from penetration through to the wearer's nose and mouth.
(See Best Cloth Masks You Can Buy for our review of masks for sale that appear to meet the WHO requirements)
Note that polypropylene, a material often used to make disposable surgical masks, has an electrostatic charge which can improve the filtration efficiency of masks. Polypropylene "spunbound" is sold in fabric and many other retail and online stores under brand names such as Oly*fun and Pellon. Polypropylene is sold in different weights (measured in grams per square meter or GSM). Most commercially manufactured surgical masks are made of 3-ply 25GSM. Polypropylene materials between 25 and 40 GSM tend to have similar filtration efficacy and breathability, while polypropylene 60 GSM has a higher filtration efficiency but less breathability (Zhao, Nano Lett 2020). Be aware that some forms of polypropylene should not be machine washed.
See below for a more detailed discussion of the filtration efficacy of various cotton and synthetic household fabrics.
Standards for masks
ASTM International, a non-profit organization that sets standards for medical masks and other personal protective equipment (PPE), has published voluntary standards for non-medical cloth face masks. Masks labeled "Meets ASTM F3502" must be shown, in an accredited laboratory, to meet one of two designations that will also appear on the mask label:
Level 1: Particle filtration efficiency of at least 20% and airflow resistance of < 15 mm H2O
Level 2: Particle filtration efficiency of at least 50% and airflow resistance of < 5 mm HH2O
(For comparison, a NIOSH approved N95 must have an airflow resistance of no more than 35 mm H2O).
Masks that claim to meet ASTM standards are also required to provide user instructions for size proper selection, proper use, and cleaning or disposal instructions.
ConsumerLab will update its mask reviews if and when ASTM Level designations become available.
How cotton and other household fabrics compare in blocking coronavirus
The first study, from the University of Illinois at Urbana-Champaign, found that many household fabrics can be as effective as the material in surgical masks for blocking droplets of sizes known to carry the COVID-19 (SARS-CoV-2) coronavirus. The blocking efficiency of a commercial medical mask was found to be 96.3%, while the blocking efficiency of a used dish cloth (85% polyester and 15% nylon) was slightly better -- 97.9%. In addition, most household fabrics were more breathable than the material in a medical mask. The dish cloth, for example, was twice as breathable as the medical mask (Aydin, medRxiv 2020 --preprint). (See the CDC website to learn how to make a cloth face covering.)
Tightly woven cotton, combined with silk or chiffon
A study at the University of Chicago and Argonne National Laboratory found that tightly woven, high-thread count cotton (600 thread-per-inch (TPI) sheet by Wamsutta) was more effective in filtering large droplets (similar to larger-sized SARS-CoV-2 droplets) than loosely woven cotton with a lower thread count (quilters cotton, 80 TPI), while fabrics with an electrostatic charge (such as silk and chiffon) were best for blocking aerosols -- the smaller sized droplets that remain suspended in air for extended amounts of time. Using layers of both fabrics, together, was most effective for blocking both large and small droplets. For example, two layers of 600 TPI cotton fabric had a large particle and small particle blocking efficacy of 99.5% and 82%, respectively, but one layer of 600 TPI cotton combined with two layers of chiffon (90% polyester, 10% spandex from Jo-Ann Stores) had a large particle and small particle blocking efficacy of 99.2% and 97% -- which, at low airflow rates (i.e., when not all air is drawn through the mask) is nearly as good as a properly-fitted N95 mask for blocking large particles and better than the N-95 with respect to small particles, of which only 85% are blocked by an N-95 mask). However, as emphasized in a published correction to the study, it is not known how efficient this fabric combination will be at normal or high rates of airflow when made into a fitted mask, i.e., when there are no leaks and all air flows directly through the mask, particularly when one is engaged in high levels of exertion. The researchers also found that small holes or leaks around the edges of the fabrics could decrease the blocking efficacy by 50% or more, and emphasized the importance of a good fit (snug and without gaps) (Konda, ACS Nano 2020). [Note: An illustration in the study shows the electrostatic layer of fabric as the inner layer when fabrics were combined. However, ConsumerLab contacted the author of the study who suggested that electrostatic fabric (such as chiffon) may be best used as the outer layer of the mask to avoid humidity from the nose or mouth, which could interfere with the electrostatic properties, but emphasized that was his suggestion, not something that was tested in the study.]
Cotton bandanas and handkerchiefs
In another study, researchers at Florida Atlantic University tested masks made from common household fabrics, as well a typical "cone" mask (often sold at pharmacies) to see how well they worked to stop droplets using a simulated model of coughing (a mannequin head through which liquid was manually pumped). Without any covering, droplets from the simulated cough traveled an average of 8 feet. With a bandana (single-layer, elastic T-shirt material, 85 threads per inch) droplets traveled an average of 3 ft. 7 inches, with a folded cotton handkerchief (as shown in this instructional video featuring the U.S. Surgeon General), 1 ft. 3 inches, and with a cone mask (CVS Cone Face Mask), 8 inches. The most effective mask was a stitched cotton mask (using two-layers of cotton quilting fabric, 70 threads per inch), with which droplets traveled just 2.5 inches. The researchers noted that "healthcare professionals trained properly in the use of high-quality fitted masks will not experience leakage to the extent that we have observed in this study. However, leakage remains a likely issue for members of the general public who often rely on loose-fitting homemade masks." (Verma, Phys Fluids 2020).
Polypropylene and surgical masks
Rather than focus on how far droplets travel, researchers at Duke looked at how well different masks block droplets during speaking. A fitted N95 mask without a valve was most effective in retaining droplets, with less than 1% of droplets being transmitted. The next most effective, in order, were a 3-layer surgical mask, a cotton-polypropylene-cotton "apron" mask, a 2-layer polypropylene mask, a 2-layer cotton pleated mask, and then an N95 with a valve.
Neck gaiters (fleece, microfiber & polyester)
The Duke researchers found that two masks offered little protection: A double-layer bandana was only slightly more effective than using no face covering at all, while the worst face covering was a "gaiter" style neck fleece (often worn during running or sports) that showed a 10% increase in the number of droplets. The researchers suggested that the neck fleece material breaks larger liquid droplets into smaller droplets than can more easily be dispersed into the air (Fischer, Sci Adv 2020 — includes photos of the masks but no details about origin or brands). However, tests conducted by researchers at Virginia Polytechnic Institute found that, when measuring droplets that dispersed in an outward direction at a distance of about 1 ft. (30 cm), neck gaiters (one made of thin, 100% polyester (Chaos) and the other, a thicker, microfiber gaiter made of 87% polyester and 13% elastane (Cirque)) worked as well as a cloth mask (a no-sew mask made of cotton T-shirt material), blocking 100% of larger droplets (> 20 microns), 90% of droplets 5 microns in size, and 50% of 0.5 micron aerosols. They were somewhat less efficient than the cloth mask at blocking smaller aerosols, although when the thinner gaiter was doubled over, it blocked about 90% of droplets and aerosols (0.5 to 5 microns) (Pan, Virginia Tech PDF 2020).
When doubled over, some neck gaiters may be more effective than a triple layer, all-cotton cloth mask. A study conducted by researchers at the CDC and National Institute for Occupational Safety and Health (NIOSH), found that a single-layer polyester neck gaiter (FKGIONG Sun UV Protection Neck Gaiter, 95% polyester, 5% Spandex) blocked 47% of outward moving cough aerosols (ranging in size from 0 to 7 microns) and when doubled over, blocked 60%. This was slightly better than a medical procedure mask with ear loops, which blocked 59% and a cloth mask made of 3 layers of cotton fabric and ear loops (Hanes Defender), which blocked 51%. An N95 respirator blocked 99% (Lindsley, medRxiv 2020 -- preprint). It should be noted that the cotton cloth mask tested did not have an outer layer made of hydrophobic material (such as polypropylene or polyester) as recommended by WHO. If wearing a neck gaiter, make sure it fits securely and consider choosing one with an adjustable cord, to help prevent it from falling down (off of the nose and mouth) during strong sudden movements, such as during a sneeze.
Which masks protect you best?
A study that evaluated how well masks protect the wearer from breathing in small particles (ranging in size from 0.02 to 0.6 microns) and factored in the fit of the mask as well as its filtration efficiency found that a NIOSH approved N95 (3M 9210) had the highest filtration efficiency at 98%, followed by 80% for a medical procedure mask with ear loops (Cardinal Health) with nylon hosiery placed over it, and 71.5% for a surgical mask with ties. [Note: The filtration efficiency of the medical procedure masks can range dramatically depending on how it was worn.] The filtration efficiency was 74% for a 2-layer woven nylon mask with ear loops (Easy Masks LLC) with an aluminum nose bridge and nonwoven filter insert which, interestingly, had a slightly higher filtration efficiency after being washed once, 49.9% for a folded, cotton bandana, 39.3% for a single-layer woven polyester/nylon mask with ties (Renfro Corporation), 37.8% for a single-layer woven gaiter/neck cover balaclava bandana MPUSA LLC), 28.6% for a nonwoven polypropylene mask with fixed ear loops (Red Devil Inc), and just 26.5% for a 3-layer woven cotton mask (100% cotton) with ear loops (Hanesbrands Inc) (Clapp, JAMA Intern Med 2020).
Best Materials for Making Your Own Mask Filter
As discussed above, the WHO recommends that the middle layer of a cloth mask be made of a synthetic, nonwoven fabric such as polypropylene, or a second layer of cotton (high thread count cotton has been shown to have better filtration efficacy than lower-thread cotton). Many cloth masks that you can buy online come with a "filter pocket" as the middle layer, which you can buy pre-made filters for, or add your own. We've reviewed common materials for making mask filters, including Filti Face Mask Material and Medline Dry Baby Wipes, as well as materials such as polypropylene and other non woven fabrics (100% polypropylene, Pellon Sew-In Interfacing and Oly*fun), cotton and quilter's cotton. Sign in as a member or join now to see our reviews and more details about materials for making your own mask filters.
Best Cloth Masks You Can Buy
If you prefer to purchase a cloth mask, we reviewed many masks sold online and identified several that we believe best meet WHO guidelines and/or are constructed with materials that offer a good combination of filtration efficacy and breathability. We also considered features that can affect fit and comfort, such as adjustable/bendable nose wires and adjustable straps, which can be particularly important for people who wear glasses or hearing aids. We also reviewed oversized masks designed to accommodate beards or to be used when singing, and masks with clear panels to enable lip reading by others.
In addition, we assessed eyeglass fogging with each mask when worn in cool air.
Our list starts with our overall Top Pick for quality, comfort and breathability, fit, and minimal eyeglass fogging. This is followed by our next favorites, as well as masks for those who need clear panels. In our review of masks, we considered those from Allet, Atelier, Giftington, Graf Lanzt, LA Linen, Proper Cloth, Rafi Nova, Stark's, Tom Bihn, Vertex, Vida, Vistaprint, and masks sold on Etsy.
Be aware that there is a shipping fee for most masks, calculated before check out based on location and/or other factors. Most companies provide an estimated time for the product to ship, but delivery time will depend on the shipping option you choose. ConsumerLab.com derives no revenue from sales of these products.
(To see our list of the best cloth masks you can buy, sign in. If you are not a ConsumerLab member, join now.)
How to reduce air leakage around a mask
Air leakage around a mask reduces the level of protection it provides you and those around you. There are several ways to reduce air leakage, as discussed below. Also be aware that if you are infectious, the area of your face beyond a leak, including eyeglasses, may become contaminated due to exhaled droplets, as demonstrated in OSHA study (Stephenson, medRxiv 2021 -- preprint).
Knotting ear loops
The fit and filtration efficiency of medical procedure masks with ear loops can be significantly improved by knotting the ear loops and then tucking in and flattening the extra material close to the face (see illustration), according to research conducted by the CDC. This was shown to reduce exposure to aerosols from a cough by 64%.
The CDC also found that wearing a three-ply cotton cloth mask over a medical procedure mask blocked 92.5% of particles emitted by a cough, while a medical mask alone blocked only 42% of particles. In addition, if a person near a coughing person double masks like this, it can reduce their exposure to particles by 82.2%, compared to a 41.3% reduction from a medical mask alone.
Be aware that, while adding a nose wire to masks can improve their fit (and therefore, possibly reduce air leakage and improve protection). They seem to be of benefit with stiffer masks but; but not with masks made with stretchy or more flexible material (O'Kelly, medRxiv 2021 -- preprint).
Try not to bend over while wearing a mask
Researchers at Columbia University who were fit testing N95 respirators found that normal breathing and talking did not negatively affect mask fit, and turning the head from side to side slightly improved fit (perhaps due to tightening). However, moving the head up and down slightly worsened fit, and bending over decreased proper fit by as much as 50%. The researchers suggested kneeling rather than bending over when wearing a mask (Chen, medRxiv 2020 -- preprint).
Masks fitters are a "frame" that can be placed over masks to improve the fit and "seal" of the mask against the face to reduce air leakage and increase inhalation filtration efficiency. Using mannequins that could "breathe," researchers at the University of Wisconsin-Madison found that placing either of two marketed mask fitters over a variety of masks increased inhalation filtration efficiencies from just 7% without the fitter to 26% for a 4-ply cotton mask, from 52% to 63% for a 3-ply spunbond polypropylene mask, from 44% to 91% for a surgical mask, and from only 18% up to as much as 95% for a 3-ply disposable non-medical mask with a melt-blown polypropylene center. Sign in to learn make a mask fitter at home or buy either of the two used in the study.
Another way to reduce air leaks was suggested by a study at Northeastern University in Boston, which showed that pulling an 8 to 10-inch tube of nylon (cut from a queen-sized nylon stocking) down over a regular mask and to the top of the neck. This significantly prevented air leakage around the mask and improved particle filtration efficiency, making the combined masking nearly as effective as an N-95 respirator which, unlike a medical mask, has an electrostatic charge and is specifically designed to prevent air leakage (Mueller, medRxiv 2020 --preprint; Godoy, NPR.org 4/22/20).
Similarly, a study found that adding a sleeve of nylon hosiery over a medical procedural mask with ear loops (Cardinal Health Inc) increased its overall filtration efficiency from just 38.5% to 80%. Other techniques that created a better fit for the procedure mask to reduce air leakage included tying the ear loops and tucking in the side pleats (see video demonstration), which increased filtration efficiency to 60.3%, or securing the ear loops with ear guards (61.7%), a hair clip (64.8%) or placing three rubber bands across the front of the mask and looped on the ears (78.2%) (Clapp, JAMA Intern Med 2020).
How to reduce eyeglass fogging from masks
Our tests indicated that eyeglasses were less likely to fog in cool air with masks that 1) came up higher on the nose and cheeks (allowing glasses to sit over the edge of the mask 2) had a bendable top frame that could be contoured for a close fit around the nose and cheeks, 3) had adjustable ear or head bands, allowing the mask to be tight against the face, and 4) had an outer layer of 100% polyester or chiffon rather than a cotton or cotton/polyester blend. Find out which masks had the least fogging.
Lens fogging may also be minimized by rinsing lenses with highly diluted liquid soap and then air drying (stand lenses up so excess drips off) (Hu, J Emerg Nurs 2020). This leaves a surfactant film that reduces surface tension and causes water molecules to spread out evenly into a transparent layer, reducing fogging (Margrain, Ann R Coll Surg Engl 2011). Anti-fogging sprays and wipes are also sold, but be sure to follow directions and allow liquids to dry before wearing to avoid eye irritation or injury from the liquid. (A CL member reported severe eye irritation after using JAWS Spit Gel which seems to have gotten into his eye after a COVID nasal test that caused eye tearing) (Peng, Cornea 2006). Eye injury has also been reported in healthcare workers in China who used anti-fog spray on medical goggles (Hu, J Emerg Nurs 2020).
Single-sided and double-sided tape strips can also be used to seal the edges of masks around the eyes and nose to reduce fogging. ConsumerLab purchased two tape strip products sold on Amazon, MaskTite Adhesive Strips and Cabeau Tape. We tried each with the masks in this review, and with a disposable mask, while wearing glasses. [Sign in to see our reviews of these tapes and our mask reviews.]
How to clean a cloth mask
The CDC advises that cloth masks be washed daily (and after high exposure) with soap and water. The agency also suggests each person have at least two cloth masks, likely so that one can be used while the other is being cleaned. It notes that "cloth can be used for an extended period as long as they are not wet or soiled, but do not reuse them unless washed and cleaned." Masks should not be worn while still wet, as the agency states that the filtration effectiveness may be reduced. The FDA recommends choosing a cloth mask that can be washed and machine dried without damage or change in shape.
Cloth masks can be washed in a washing machine. They can also be cleaned using heat, but a washing machine is preferred. Silk and chiffon fabrics may need to be hand washed with cold water.
If you've purchased a mask, check with the fabric manufacturer or see the care instructions on the label. If hand washing is required, be sure to use adequate soap/detergent and rinse thoroughly, as soap helps to break down the lipid layer that allows SARS-Cov-2 to attach to surfaces. Some sturdier silk and chiffon blends, such as poly-spandex-chiffon, can be machine washed with warm water and tumbled dry if placed in a mesh bag for delicates.
Currently, the CDC recommends re-using a single N95 respirator no more than five times. It also advises healthcare workers "wear one N95 FFR each day and store it in a breathable paper bag at the end of each shift with a minimum of five days between each N95 FFR use, rotating the use each day between N95 FFRs," noting that this "will provide some time for pathogens on it to "die off" during storage."
A study of 3M N95 respirators (dome-shaped duckbill models) worn by healthcare workers at Johns Hopkins Hospital caring for COVID-19 patients found that all N95s worn less than 12 times (and stored between uses) passed seal check and fit testing. Even when used about 40 times, 83% still passed these tests. The study implied that the masks had not been subject to decontamination procedures but they may have been somewhat protected from pathogen contamination as they were typically worn with face shields (Fabre, medRxiv 2020 -- preprint).
Effect on breathing function and potential carbon dioxide buildup
When wearing an N95 respirator or a well-fitted mask with high blocking efficiency there can be some carbon dioxide buildup inside the mask over time (Sinkule, Ann Occup Hyg 2013). According to researchers at Stanford University, N95 masks are "are estimated to reduce oxygen intake by anywhere from 5 to 20 percent. That's significant, even for a healthy person. It can cause dizziness and lightheadedness." However, a small study in the U.S. found that wearing an N-95 mask for up to one hour did not cause any significant adverse effects in healthy healthcare workers performing moderate activities, despite significantly decreased inhaled oxygen and increased inhaled carbon dioxide levels (Roberge, Respir Care 2010). A representative from the CDC told Reuters.com that "...the level of CO2 likely to build up in the mask is mostly tolerable to people exposed to it. You might get a headache but you most likely [would] not suffer the symptoms observed at much higher levels of CO2. The mask can become uncomfortable for a variety of reasons including a sensitivity to CO2 and the person will be motivated to remove the mask. It is unlikely that wearing a mask will cause hypercapnia [elevated blood levels of carbon dioxide]."
On the other hand, surgical masks (also known as medical masks), which are inherently not as well-fitting as N95 respirators, do not lead to CO2 intoxication or oxygen deficiency, as noted by the World Health Organization. Several studies have demonstrated this. For example, a study among 20 healthy adults showed that moderate exercise (walking on a treadmill) for one hour while wearing a surgical mask led to only slight, clinically non-significant changes in CO2 levels (as measured on the skin) compared to exercise without a mask (Respir Physiol Neurobiol 2012). Even during vigorous exercise (cycling to exhaustion, an average of about 10 minutes) a study among 14 healthy men and women showed that wearing a disposable surgical mask or a three-layer cloth mask (Washable 3D Face Mask, TriMax Sports Inc. — made with bamboo charcoal cloth, non-woven fabric, and Lycra) had no effect on blood or muscle oxygenation or exercise performance compared exercising without a mask (Shaw, Int J Environ Res Public Health 2020).
Furthermore, a study of 10 healthcare workers (including individuals with controlled asthma and four smokers), found that wearing a surgical mask (AFLUID, made of three layers of polypropylene and one layer of liquid resistant polyethylene) continuously for four hours did not reduce breathing function (Ciocan, Med Lav 2020). Additionally, older adults who wore a three-layer disposable nonmedical face mask with ear loops (Boomcare DY95 model, Deyce Leather Co Ltd) for one hour showed no decline in self-reported blood oxygen levels (as measured by pulse oximeter) (Chan, JAMA 2020).
Another study showed that, even among older adults (average age 71) with breathing difficulty due to severe chronic obstructive pulmonary disease (COPD), wearing a surgical mask during a six-minute walk test did not result in any major changes in CO2 retention (Samannan, Ann Am Thorac Soc 2020). The researchers suggested that discomfort while wearing a surgical mask might be caused by the increased warmth of facial skin and inhaled air inside the mask, which may trigger sensations of anxiety or claustrophobia in some people.
The CDC advises that face masks should not be placed on children under the age of two, anyone who has trouble breathing, or anyone who would not be able to remove the mask without assistance.
Inhalation of microplastics
Concern has been raised about the risk of inhaling microplastic particles when wearing a mask made of polypropylene or other materials containing plastics. A study in China found that most masks increased the inhalation of fiber-like microplastics but notably decreased the risk of inhalation of spherical particles. While some evidence has suggested that fiber-like microplastics may be more toxic to animals than spherical microplastics (Ziajahromi, Environ Sci Technol 2017), the investigators concluded that, overall, inhalation of microplastics from masks is a small problem compared to the risk of spreading COVID-19 without a mask, as people already regularly inhale high amounts of microplastics from the air, with or without a face mask.
The study found that only N95 respirators reduced the risk of inhaling fiber-like microplastic particles compared to not wearing a mask, while a nonwoven mask, a fashion mask, and a cotton mask increased it by 17%, 41%, and 54%, respectively, surgical masks increased it by about 4% to 73%, and activated charcoal mask increased it by 117%. Inhalation of spherical microplastic particles was reduced by about 47% to 96% for all masks compared to not wearing a mask.
Disinfecting any of the masks with UV irradiation, alcohol, air blower treatment, washing with soap and water, or exposure to sunlight increased the microplastic inhalation risk compared to untreated masks, although the risk was only small following washing with water and was lowest following exposure to sunlight. Alcohol disinfection increased the risk of microplastic inhalation most significantly (Li J Hazard Mater 2020).
Are KN95 respirators as good as N95s?
N95 and KN95 masks (or, more technically, respirators) are designed to protect you, as well as others around you. Both are supposed to filter 95% of particles down to 0.3 microns. However, as discussed below, this isn't always the case with widely sold KN95 masks (which are designed to meet Chinese, rather than U.S. specifications). In addition, while N95 respirators attach with head bands to help ensure the best fit, most KN95s attach with ear loops, which may cause a loose or improper fit, and allow for air leakage. A study of N95 and KN95 respirators have shown that mask performance depends, in part, on the tightness of the contact between the material and the facial skin and masks that tied around the head outperform those with elastic ear loops (Sickbert-Bennett, JAMA Intern Med 2020). As discussed above, how you move while wearing a mask may also affect fit.
Nevertheless, due to the shortage of N95 masks, the Occupational Safety and Health Administration (OSHA) provided guidance in April of 2020 that KN95 masks certified to China's GB2636 standards of 2006 or 2019 (imprinted on masks as "GB2626-2006" or "GB2626-2019") "will provide greater protection than surgical masks (i.e., facemasks, other than surgical N95s), homemade masks, or improvised mouth and nose covers, such as bandanas and scarves." Caution: You should not buy a KN95 mask that does not have its GB2626-2006 or GB2626-2019 imprinted on it.
Tests of KN95s from China by the CDC show that the filtration efficacy of some KN95 masks is 95% or higher but can be as low as 5.3%. Furthermore, tests by ECRI, an independent, U.S. based non-profit organization that evaluates equipment for hospitals and healthcare systems, showed that 5 of 11 KN95s did not meet the filtration efficiency standard of 95%. ECRI also found large variations in filtration efficiencies of KN95s within the same lot from a single manufacturer, suggesting quality control issues. (You can download ECRI's test results, which includes manufacturer information and photos of the respirators tested by clicking on "PPE Testing Report" on this page on ECRI's site).
Buying an KN95
The FDA has published a list of N-95 and KN95 respirators from China that have emergency use authorization (EUA) from the FDA during the pandemic. These have not gone through the CDC (NIOSH) approval process but some have since been tested by the CDC, and the FDA subsequently removed a number of respirators from the EUA list that did not perform well in the CDC's tests. Those that have been removed from the FDA's EUA list and are no longer authorized are shown underneath the list of authorized respirators.
Finding the Best KN95 Mask
N95 masks are currently very hard to find and purchase as they remain reserved for healthcare and frontline workers. In contrast, KN95 masks are widely available for purchase on websites such as Amazon. However, it can be very difficult to know if a KN95 mask is genuine and effective. We reviewed many KN95 masks sold on Amazon but found only one currently on the FDA's list of authorized respirators that we recommend, and we found two that should be avoided. We also found an FDA-authorized KN95 through an online direct distributor in the U.S. Sign in to get the details and see our Top Picks.
The CDC publishes a list and images of dozens of counterfeit and falsely marketed respirators. Signs of a counterfeit respirator include no approval number or NIOSH markings, decorative fabrics or add-ons, and claims of being approved for children.
According to the United States Department of Labor, healthcare workers who are unable to obtain N95 respirators may use R95, R99, P95, P99, P100 and others respirators. Like N95 masks, these are expected to filter out a minimum of 95% of particles of the most penetrating size, and those ending in a "99" or "100" filter out at least 99% or 99.97%, respectively, of such particles but can be more difficult to breathe through. R95 and P95 masks are typically used for protection when working with oil-based substances like fuel, paints, solvents, or pesticides. N95s are not resistant to oil, R95s are "somewhat resistant" and P95s are "strongly resistant to oil or oil proof," as shown in the CDC's infographic about these types of masks. If considering an alternative respirator, make sure it is NIOSH approved. Respirators with exhalation valves should not be used when trying to protect others. (See a video demonstration by researchers at Florida Atlantic University of how aerosols can spread when coughing while wearing an N95 mask with a valve).
KF94 respirators from Korea are often promoted as the Korean "equivalent" to N95 respirators, but this is not quite accurate. Although they can have relatively high filtration efficacy, KF94 masks are considered "public use" respirators and are not held to the same performance standards as Korea's Special 1st class "occupational use" respirators (which are considered to be roughly equivalent to NIOSH approved N95 masks). KF94 respirators are designed to have a filtration efficacy of 94%, and CDC tests of one brand of KF94 found its filtration efficacy to be even higher (99.85 to 99.94%). However, unlike all NIOSH-approved N95s (which attach with head bands), KF94 respirators attach with ear loops, which, the CDC points out, may compromise their fit and efficacy. The CDC did not perform fit testing on the KF94s it tested and noted a lack of information about manufacturing quality control. In addition, unlike surgical N95 respirators, KF94 respirators are not considered fluid resistant (Kim, J Korean Med Sci 2020).
Electrical air purifying respirators that mimic powered air-purifying respirators (PAPRs) are available on Amazon, ranging in price from about $60 to $100, but these devices would not be suitable for preventing the spread of COVID-19 among the general public. These devices include a portable high efficiency (HE) filter that can be connected to a face mask via a flexible hose/air duct to supply fresh air to the wearer. By ventilating air from the HE filter to the mask, these devices should create positive air pressure. This means that air exhaled by the wearer would leak out of the mask. Consequently, these devices might protect the wearer if the ventilation is strong enough, but they would not protect individuals nearby the wearer.
Furthermore, unlike NIOSH-certified PAPRs, which are rated as being more effective than N-95 masks, available electrical air purifying respirators do not appear to be certified. Therefore, it is uncertain if these devices even help protect the wearer. In addition, similar to other personal ("wearable") air purifiers, these devices might not be permitted on airplanes, as security officers can confiscate these devices if they feel they are unsafe or cause a threat.
Are copper masks better?
Copper has been shown to inactivate a wide variety of bacteria and some viruses, typically within minutes to hours of contact, and a study found that SARS-CoV-2 (at about 72°F and 40% relative humidity) was undetectable on copper after four hours (van Dormalen, NEJM (correspondence) 2020). There do not appear to be studies showing how effective masks made with copper or copper infused fabric are against SARS-Cov-2. However, preliminary research with other viruses suggests a possible benefit. A study funded by the maker of copper masks (Cupron) for healthcare and institutional use, showed that an N95 mask with two added layers of copper oxide infused material (polypropylene fabric containing 2.2% weight/weight copper particles) had a similar filtering efficacy as a regular N95 mask, but was much more effective in inactivating human influenza A virus (H1N1) and avian influenza virus (H9N2) (Barkow, PLoS One 2010). A University of Massachusetts Amherst microbiologist developed a reusable mask made of 99.95% pure copper mesh, which, according to a university news release, was shown to "kill 90% of microbes within five minutes of contact." In Hong Kong, the government is distributing fabric masks to the public that contain copper, known as the CuMask+ (Parry, BMJ 2020). According to the manufacturer, CuMask+ is made up six layers, "two of which are specially made with small quantities of copper." Tests published by the company suggest it retains antiviral activity with up to 60 washes (handwashed with soap and cold water). If you use a copper-containing mask, be sure to clean it regularly and according to the product instructions: Bacteria and viruses can cling to dirt or other particles on copper, making it less effective (Grass, Appl Environ Microbiol 2011).
Some concerns have been raised about the safety of copper masks and the possibility of breathing in copper particles. While we don't have safety information for specific products, laboratory studies that measured the amount of copper released from copper oxide impregnated masks during 5 hours under simulated breathing conditions was far below the respiratory copper permissible exposure limit (PEL) set by the USA Occupational Safety and Health Administration ("OSHA") (Borkow, Curr Chem Biol 2012).
How to protect yourself from COVID-19 in a car
Preliminary research suggests that viral loads can quickly build up within a closed car, even during rides as brief as 15 minutes. Wearing a mask, as well as a face shield, are good first steps to help protect yourself and others. When there are two people in a car (one driver and one passenger) seating the passenger in the back seat on the opposite side of the driver creates the most distance between them. To increase ventilation, computer modeling research shows that riding with all windows down is most effective. Since this isn't always practical, the next most effective way to increase ventilation is by opening one window in the back and one in the front, opposite of where the occupants sit, creating airflow across the interior of the car. Keeping all the windows closed and running the air-conditioning, is least effective (Mathai, Sci Adv 2020). Keep in mind that none of these steps eliminate the risk of infection.
How to improve safety for bus passengers and drivers
A study of aerosol flow on a school bus and transit bus that were driven under real-world conditions showed that mask wearing and ventilation can significantly reduce exposure to aerosols for passengers (Edwards, medRxiv 2021 -- preprint). Based on their experiments, the researchers recommended the following tips to help reduce exposure to aerosols for bus passengers:
- Require all passengers and drivers to wear masks on buses. Even a cloth mask that's 50% efficient can reduce particles released from a cough by 50% and reduce their dispersal by several feet.
- Open windows partially or fully. This can reduce airborne particles by 50% to 80%.
- Consider seating arrangements that only allow for same household or same cohort passengers to sit together.
- Social distancing of six feet is not practical on most buses, but any extra distance allows the air movement to reduce exposure to infectious particles.
What masks protect against wildfire smoke?
Cloth masks, including those with sewn-in or removable filters, should not be relied on for protection from wildfire smoke, according to the CDC. They protect against some of the larger particles in wildfire smoke, but not from smaller particles in smoke that can damage the lungs. In addition, one-strap paper dust masks and surgical masks, worn alone, are not recommended for wildfire smoke protection.
It is recommended that people who have to be outdoors in wildfire affected areas wear fit-tested, NIOSH-approved N95 or P100 respirators, and the CDC notes that properly fitted N95 respirators can "provide protection from wildfire smoke and from COVID-19 for the individuals wearing them." To help prevent the spread of COVID-19 to others, N95 masks without valves are recommended. If an N95 mask with a valve is your only option for wildfire smoke protection, consider covering the valve with tape or wearing a surgical mask over the N95 when around others, as recommended by John Balms, M.D. at UCSF.
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