Scientists suggest how to choose a mask when the virus strikes.

2020-01-22 | Back to Park original |

New type of coronavirus is coming, "mask" has become a hot search term. We invite scientific researchers to explain the correct selection and wearing method of mask.

If you have limited time, please see the quick question and answer; for the cause and effect, please read the text.

1. Is it really useful to wear a mask?

Useful! But wearing a mask and washing your hands at the same time, both are indispensable.

2. Types and uses of masks

Recommendation: N95 with or without breathing valve and surgical masks. From the design, according to the wearer's own protective ability ranking high to low: N95 masks> surgical masks> ordinary medical masks> ordinary cotton masks.Virus carriers should use N95 masks without a breathing valve.

3. How should I use a mask?

Wash your hands before wearing, fit your face tightly, the colored side is washed out, and the metal strip is on it.

4. How to deal with used masks?

Answer: Masks cannot be shared. If they are damaged and dirty, and they have difficulty breathing after wearing, they need to be replaced with new masks. Discard used bags and wash hands or disinfect them immediately.

5. Is N95 disposable? Can I reuse it?

Answer: Not recommended, but if it is necessary, store it in a clean, ventilated container such as a clean paper bag if there is no pollution; minimize cross-contamination.

6. How effective is PM2.5 mask, can it be used to prevent virus infection?

Answer: "PM2.5 mask" is not precise. For specific analysis of different haze masks, please check the product specifications carefully.

7. Will the mask expire?

Answer: Most disposable N95 respirators have a shelf life and are related to storage conditions.

When the new coronavirus broke out, the masks were out of stock again. There was even a new type of purchasing in the circle of friends: mask purchasing.

Small masks, do you really understand? What are the types of masks? What are the differences? Which mask is the best to block the spread of virus? Do we have to buy N95 masks? N95 breather valve will be reducedProtective effect? ​​This article summarizes eleven questions about masks. I hope you can clear up doubts about masks in this virus-ridden season.

1. Is it really useful to wear a mask?

The answer is beyond doubt: useful.

Whether from an epidemiological perspective or from a clinical research standpoint, there is already a lot of evidence to prove that wearing a mask properly can effectively prevent the spread of the virus.

The first clinical study was published in the International Journal of Infectious Diseases in 2008. The study concluded that, when used correctly, masks can effectively prevent the spread of the virus[1]. Children with influenza at home, if the masks can be used correctly, the family is 80% less likely to be diagnosed with the virus, and in this study, the differences between different masks are small.

Another study published in the Annals of Internal Medicine reported similar results. The researchers investigated 400 flu patients. They found that families of these patients who frequently wash their hands and wear surgeryMasks reduce the risk of flu by 70% [2].

There are other studies that have found that even in other environments outside the home, good hygiene and wearing a mask can help reduce the risk of infection.

A study conducted a randomized trial of more than 1,000 students living in university dormitories. Researchers divided students into the following groups: the mask-wearing group, the mask-wearing and frequent hand-washing group, and the non-mask-wearing group.The results showed that those who wear masks and wash their hands frequently have a 75% reduction in the risk of flu-like illness [3]. At the same time, the study also found that using masks alone but not washing their hands frequently did not reduce the risk. So wearing a maskFresh hands and regular hand washing are both necessary.

2, how to wear a mask correctly

It is not as long as putting on a mask, you can have nothing to worry about and stay away from the virus. The correct wearing method recommended by the Health and Epidemic Prevention Center of the Hong Kong Department of Health should be divided into "select-wash-confirm-mask-stick"Five steps [4].

① Choose: choose a mask that fits your face size;

② Washing: You must clean your hands before wearing a mask;

③ Yes: determine the integrity of the mask, front and back, and up and down direction, for example, the colored side should be outward, and the metal strip should be upward;

④ Cover: cover the nose, mouth and chin tightly;

⑤ Adhesion: If there is a metal strip edge, it should be pressed by hand along both sides of the bridge of the nose to ensure that it is tight.

The picture below shows the five-step wearing method of wearing a mask after washing your hands.

Figure 1. Correct wearing method of the mask author modified from the original network picture

Remind everyone to pay more attention to the step of washing hands. In daily life, most people ignore the step of washing hands when wearing a mask: not only to wash hands before wearing, but to avoid touching the mask again with hands after wearing, andClean your hands before and after touching again, which will help improve the protective effectiveness of the mask.

3.Types and uses of masks

In English, there are actually two types of masks: masks and respirators. The N95 masks that have recently been hung by your mouth are common respirators.

The pneumonia epidemic caused by the new coronavirus is very serious, and everyone buys masks just in case. Combined with recent discussion hotspots and considering whether it is easy to buy, we list the following common masks see the table below, Compared their uses and filtering effects.

Table 1. Classification and precautions for common masks. Click to view larger image data compiled from references [9] [10]

The filtering effect of various masks is closely related to the size of the particles you want to filter. The popular coronavirus particles this time are spherical and have a diameter of about 0.125 microns [5, 6], but viruses usually rely on droplets, dust, etc.Small particles are transmitted. Human-made droplets such as those produced by breathing, talking, sneezing, and coughing include various cells, physiological electrolytes in mucus and saliva, and potentially various infectious agents such asBacteria, fungi, viruses, etc.. Naturally occurring droplets vary in size. Published data suggest that sneezing may produce up to 40,000 droplets with diameters between 0.5–12 microns [7,8].

4, the difference between ordinary masks, surgical masks and N95 masks

1 mask

Ordinary masks, also known as masks, are loose, disposable devices that form a physical barrier around the wearer's mouth and nose to isolate potential contaminants in the surrounding environment. Different masks have different uses and thickness, The protection effect on people is also different, and the degree of wearing comfort is also different.

Common cotton masks and sponge masks are very simple. They are made of different fibers and have limited protection. Most surgical masks are self-priming filter masks. The working principle is to allow harmful air to pass through.The filter material of the mask is inhaled or exhaled after filtering. The filter mechanism of the mask material is mainly the following Figure 2 :

Figure 2. Schematic diagram of filtering mechanism of common medical mask filter material Image source:

Surgical masks are mentioned here. Standard surgical masks are divided into 3 layers: the outer layer is a water blocking layer to prevent liquid splashing, the middle layer is a filter layer, which can block 90% of 5 micron particles, and the inner layer is for absorptionLiquid and moisture released by the wearer Figure 3. Surgical masks are suitable for basic protection of medical personnel or related personnel.

Figure 3 Composition of common surgical masks Image source:

If worn properly, surgical masks can prevent large particles of droplets, sprays, or splashes containing viruses and bacteria from entering the nose and mouth. It also helps to reduce splashes of saliva and respiratory secretions on others, thereby preventing infectionHowever, by design, surgical masks cannot filter or block small less than 5 micron particles in the air, which may be transmitted by coughing, sneezing or certain medical procedures. Due to surgical masks and faceThe stickers are loose and not tight, so surgical masks cannot completely protect bacteria, viruses and other pollutants from entering the wearer's nose and nose.

Figure 4. Common surgical masks similar to ordinary medical masks, but better filtering

In short, ordinary masks have no filter material; surgical masks have filter material, but cannot filter very small <5 microns particles.

2 N95 mask

N95 mask is actually a respirator. Respirator is a kind of respiratory protection equipment. It is designed to fit the face more closely than ordinary masks, and can effectively filter particulates in the air. Among them, NMeans Not resistant to oil, can be used to protect non-oily suspended particles; 95 means that the filtration efficiency is greater than or equal to 95%, indicating that after careful testing, this respirator can block at least 95% of very small 0.3 micron levelTest particles. If worn correctly, the N95's filtering capacity is better than the ordinary masks and medical masks mentioned above. However, even if the requirements are fully met, the risk of infection or death will not be 100% eliminated.

To effectively function, we need to choose an N95 mask that suits your face shape. Before use, check whether it is suitable. Wear a respirator and adjust the rubber bands to make the respirator fit the face tightly, but not feel uncomfortable..It is recommended to read the instructions carefully to see what different manufacturers have suggested for a "good fit."

Usually, the US Centers for Disease Control and Prevention CDC does not recommend the use of face masks and respirators in home or community settings. However, during public health emergencies, such as when a virus is circulating,For people infected with the flu or other respiratory diseases, the US FDA has approved the following four models Figure 5 :

3M Particle Respirator 8670F

3M particulate respirator 8612F

Pasture Tm F550G respirator

Pasture Tm A520G

Figure 5. Four types of N95 masks approved by the US FDA

5. Are there any pros and cons of disposable masks? Will wearing pros and cons affect the prevention effect?

As mentioned above, surgical masks are divided into three layers: inside, outside, and inside. Ordinary disposable masks should also have front and back sides. Usually, the outer layer prevents liquid from splashing, and the inner layer is absorbent and soft surface.It will not only affect the effectiveness, but also affect the wearing comfort. You can check whether you are wearing correctly according to the following methods :

Touch feeling: soft water-absorbing surface is facing in, rough waterproof surface is facing out

Metal edge of the bridge of the nose: The exposed side of the metal faces outward, and the wrapped side faces inward

Ear hanging line: the line of the general tailor is outside

look at the color: generally white is inward, the colored part is outward

6. Will the exhalation valve affect the protective effectiveness of the N95 mask?

Maybe some friends noticed that N95 is divided into two types with or without exhalation valve. For people with chronic respiratory disease, heart disease or other diseases with dyspnea symptoms, using N95 respirator may make the wearer breathe moreDifficult, so using N95 masks with an exhalation valve makes it easier for them to exhale and helps reduce heat build-up.

The exhalation valve design is very delicate. There are several layers of mouthpieces. The mouthpieces will be closed tightly when inhaled to ensure that no particles enter. When exhaled, the mouthpieces will be opened to let the hot and humid air out. At the same time, there is stillLayer of soft mouth cover to ensure that no small particles enter.

In the past two days, people have a lot of misunderstandings about the N95 with an exhalation valve. Some people think that there is no protection for the exhalation valve. A study published in 2008 specifically investigated whether the exhalation valve would affect the wearer.The conclusion is that the presence or absence of an exhalation valve does not affect the respiratory protection of the wearer. [11] Simply put, N95 with an exhalation valve can protect the wearer, but not the surrounding people. If you are a virusCarriers, please choose N95 without exhalation valve, do not spread the virus. If you want to maintain a sterile environment, you cannot use N95 with exhalation valve, because the wearer may exhale bacteria or virus.

Figure 6. Study of whether the exhalation valve will affect the protective effect on the wearer

7, Is N95 disposable? It is expensive, can I reuse it?

In fact, all FDA-approved N95 respirators are single-use. There is no way to determine the maximum number of safe re-use of N95 respirators under any circumstances. Whether N95 can be safely reused is affected by many factors such as the risk of infectionImpact. However, under special circumstances, N95 is difficult to purchase and expensive, and is limited by the shortage of masks. Unless the mask ’s data sheet specifically emphasizes "only a single use", it can be considered for repeated use in daily use, but this practiceThere are risks. The most obvious point is that the outside of N95 has actually been contaminated, but the user has not realized that repeated use has the risk of infection. If the conditions are limited, it is really necessary to repeat the use, you need to pay attention to several points [12] :

① Make sure the used N95 respirator cannot be contaminated.

② Hang the used N95 respirator in the designated storage area, or put it in a clean, breathable container, such as a paper bag. To minimize potential cross-contamination, please store the respirators separately to avoid each otherContact and clearly identify the person using the respirator. Storage containers should be handled or cleaned regularly.

③ Before and after touching or adjusting the respirator, clean your hands with soap and water or alcohol-based hand sanitizer.

④ Avoid touching the inside of the respirator. If you accidentally touch the inside of the respirator, clean your hands as described above.

⑤ If the N95 respirator is damaged or soiled, or if you feel it is difficult to breathe after wearing it, you should remove it. The method of safely discarding N95 is similar to that of a mask: put it in a plastic bag, and then put it in a trash can. After disposalWash your hands.

8, are N95 masks the same as surgical masks?

A two-day article published online in the JAMA magazine in 2019 that compared the efficacy of surgical masks and N95 respirators in preventing influenza or other viral respiratory diseases [13].

This new study was conducted at multiple medical centers in seven cities in the United States. Researchers collected nearly 2,400 medical staff wearing surgical masks or N95 respirators during the four flu seasons from 2011 to 2015.And other acute respiratory diseases. The conclusion is: there is no significant difference in the preventive effect of these two types of masks, which are several times less expensive.

Some previous studies in the laboratory environment have shown that N95 respirators can provide better protection against acute respiratory infections than surgical masks. However, in clinical settings, randomized controlled trials of N95 respirators andDoes not show the same benefits. [14] Although this 2019 study is currently the largest, it is too early to conclude from the results of one trial alone, as these trials did not ensure correct wearing. EventuallyThe conclusion needs further proof.

A 2012 study found that a face-fitting mask can provide about 94% protection against airborne viruses, and a N95 respirator that is properly worn and fits tightly to the face can achieve an optimum of greater than 99%Protection [15]. But wearing any kind of mask loosely can only achieve 60% protection.

So, in theory, wearing N95 correctly provides more comprehensive protection. But if you ca n’t wear N95 for various reasons, surgical masks are also a good choice.

9. Can PM2.5 masks prevent virus infection?

PM2.5 refers to particles with a diameter of 2.5 microns or smaller, and the term “PM2.5 masks” is not strict. Different haze masks should be analyzed on a case-by-case basis. For example, our commonly used 3M9001 andThe 3M9002 foldable respirator mask with valve Figure 7 complies with the requirements of GB2626-2006 KN90, which means that it can block at least 90% 0.3 micron level of test particles in the particle test experiment.Although the effect is slightly inferior to N95, it is much better than ordinary disposable masks. The 3M8210, which is recommended by more people, conforms to the KN95 standard itself, so it can be used to prevent virus infection..

Figure 7. Two Foldable Anti-Particulate Masks with Valves picture from the Internet

Overall, if you don't know how to deal with the "PM2.5 mask" in your opponent, it is recommended to check its product specifications before judging whether to continue using it.

10. What should I do after using a mask?

Disposable masks cannot be shared, and re-use is generally not recommended see Article 7. If your mask is damaged or soiled, or if it is difficult to breathe through it, you should replace it with a new mask. If you are inIn an infectious environment, please wrap it up and discard it, or throw it in a garbage bin in the hospital for infectious waste, and wash your hands or disinfect it immediately. Even if there is no infectious problem, it is recommended to protect yourself and others.Put it in a plastic bag and put it in the trash. Also, remember to wash your hands and disinfect after handling.

11. Will the mask expire?

Most disposable N95 respirators have a shelf life, which is also related to storage conditions.

Why a mask expires? Because the components of a mask will degrade over time, affecting its function. Over time, components such as masking straps and filter membranes may age, which affects the matching and sealing of the face.Quality. In addition, expired respirators may no longer meet certification guidelines set by the National Institute for Occupational Safety and Health NIOSH.

Different types of respirators, filter media, other materials used, and manufacturing dates will have different expiration dates.

Storage conditions are also the key factors affecting the shelf life. When storing, you should pay attention to the following two points :

① Always keep the respirator in the original packaging

② The place to store the respirator should avoid contaminated areas, dust, direct sunlight, extreme temperatures, excessive humidity and harmful chemicals

For other types of masks, please also refer to the product description you purchased to ensure that it is used within the validity period.


I have written here, I believe everyone has also understood that, from the design, if you rank according to the wearer's own protective ability priority high to low: N95 masks> surgical masks> ordinary medical masks> ordinary cotton masks.

If you are a virus carrier, please choose N95 without exhalation valve, don't spread the virus. Please remember to buy a regular production N95 that meets the test standards!

Figure 8. Priority ranking of different masks on the wearer's own protection ability

Coronaviruses are transmitted from person to person, usually when someone comes into contact with the secretions of an infected person. The infectivity of the virus directly affects the route of transmission. The current transmission of new types of coronavirus is unclear,However, according to past experience, contact with infected body fluids caused by coughing or sneezing, or shaking hands with the infected person may lead to infection. If your hand touches what the infected person touched, then touch your own mouth, noseOr eyes, it can also be infected.

Masks are not a panacea, but wearing masks properly and washing your hands frequently to disinfect them can greatly reduce the chance of being infected. You can choose the mask that suits you best according to your environment probability of infection.Best, but it is not suitable for everyone. Many people feel uncomfortable wearing N95 and can't stick to it. In this case, it is better to choose surgical masks. Wearing masks is worse than not.

Finally, go out less, do n’t go to a crowded place! I hope everyone can be safe, if you have any questions, you can post them in the comment area, and we will try to answer them for you!

Writing | Shi Yan, Ji Zhi Girl


[1] CR MacIntyre et al., The First Randomized, Controlled ClinicalTrial of Mask Use in Households to Prevent Respiratory Virus Transmission. International Journal of Infectious Diseases 12, e328 2008.

[2] BJ Cowling et al., Facemasks and Hand Hygiene to Prevent Influenza Transmission in Households: A Cluster Randomized Trial. Annals of Internal Medicine 151, 437-446 2009.

[3] AE Aiello et al., Facemasks, Hand Hygiene, and Influenza among Young Adults: A Randomized Intervention Trial. PLOS ONE 7, e29744 2012.


[5] M. Bárcena et al., Cryo-electron tomography of mouse hepatitisvirus: Insights into the structure of the coronavirion. Proceedings of the National Academy of Sciences 106, 582-587 2009.

[6] BW Neuman et al., Supramolecular Architecture ofSevere Acute Respiratory Syndrome Coronavirus Revealed by ElectronCryomicroscopy. Journal of Virology 80, 7918-7928 2006.

[7] EC Cole, CE Cook, Characterization of infectious aerosols inhealth care facilities: An aid to effective engineering controls and preventivestrategies. American Journal of Infection Control 26, 453-464 1998.

[8] JW Tang, Y. Li, I. Eames, PKS Chan, GL Ridgway, Factorsinvolved in the aerosol transmission of infection and control of ventilation inhealthcare premises. Journal of Hospital Infection 64, 100-114 2006.

[9] Guidelines for Technical Review of Medical Mask Product Registration


[11] S.-A. Lee, SA Grinshpun, T. Reponen, Respiratory PerformanceOffered by N95 Respirators and Surgical Masks: Human Subject Evaluation withNaCl Aerosol Representing Bacterial and Viral Particle Size Range. The Annalsof Occupational Hygiene 52, 177-1852008.


[13] LJ Radonovich, Jr et al., N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial. JAMA 322, 824-833 2019.

[14] JD Smith et al., Effectiveness of N95 respirators versus surgicalmasks in protecting health care workers from acute respiratory infection: asystematic review and meta-analysis. Canadian Medical Association Journal 188,567-574 2016.

[15] JD Noti et al., Detection of infectious influenza virus in coughaerosols generated in a simulated patient examination room. Clinical infectiousdiseases: an official publication of the Infectious Diseases Society of America 54, 1569-1577 2012.

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