The most detailed in history! Confusion about masks, it is enough to read this article - Protective Equipment

The most detailed in history! Confusion about masks, it is enough to read this article

The new coronavirus is attacking, and the “mask” is out of stock overnight, making it difficult to buy with money. But little masks, do you really understand? What kinds of masks are there? What is the difference? Which mask is best for blocking the spread of the virus? Do I have to buy N95 masks? Can it be reused? Will the exhalation valve reduce the protective effect… We have summarized 11 key questions and answers about masks, hoping to sweep away the doubts about masks in this viral season.

  1. Is it really useful to wear a mask?

  The answer is unquestionable: it really works!

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

  Published in “International Journal of Infectious Diseases” in 2008. A clinical study concluded that, when used correctly, masks can effectively prevent the spread of the virus. If there are children with flu at home, if the masks are used correctly, the possibility of family members being diagnosed with the virus is reduced by 80%.

  Another study published in the Annals of Internal Medicine reported similar results. Researchers surveyed 400 influenza patients. They found that if the family members of these patients frequently wash their hands and wear surgical masks, the risk of flu is reduced by 70%.

  However, researchers have also found that using masks alone does not wash hands often and does not reduce the risk. Therefore, it is necessary to wear a mask and wash your hands at the same time.

  2. How to wear a mask correctly

  It’s not that as long as you put on a mask, you can worry-free and stay away from viruses. The correct wearing method recommended by the Health and Epidemic Prevention Center of the Hong Kong Department of Health should be divided into five steps: “select-wash-confirm-cover-paste”.

  ① Choose: Choose a mask with the right size for your face;

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

  ③ Indeed: Determine the integrity of the mask, the front and back sides and the up and down direction, for example, the color side should be outward, and the metal strip should be upward;

  ④ Cover: The nose, mouth and chin should be tightly covered;

  ⑤ Sticking: those with metal strips should be pressed by hand along both sides of the nose bridge to ensure tightness.

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

The correct way to wear the mask (Photo source: The author of Huipu official account is modified from the original image on the network)

  Once again remind everyone to pay more attention to this step of hand washing. In daily life, most people ignore the step of washing their hands when wearing a mask: not only to wash their hands before wearing, but also to avoid touching the mask with their hands again after wearing them, and clean them before and after touching again. With both hands, this helps increase the protective effectiveness of the mask.

  3. Types and uses of masks

  The masks we usually say are actually divided into two types: masks and respirators. N95 masks, which are recently hung by everyone’s mouth, are common respirators.

  Combined with recent hot spots, and considering whether it is easy to buy, we list the following common masks (see table below) and compare their uses and filtering effects.

Common masks classification and precautions for use (Photo source: Huipu official account)

  The filtering effect of various masks is closely related to the particle size to be filtered. The current coronavirus particles are spherical, with a diameter of about 0.125 microns, but the virus is usually spread by small particles such as droplets and dust. Droplets naturally produced by humans (such as those generated by breathing, talking, sneezing, and coughing) include various cells, physiological electrolytes in mucus and saliva, and potentially various infectious agents (such as bacteria, fungi, and viruses) ). Naturally generated droplets vary in size. Published data indicate that sneezing may produce up to 40,000 droplets with a diameter between 0.5–12 microns.

  4. The difference between ordinary masks, surgical masks and N95 masks


  Ordinary masks, also called face 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, different thicknesses, different protective effects on people, and different wearing comfort levels.

  The common cotton masks and sponge masks are very simple, made of different fibers, and have limited protection. Most surgical masks are self-priming filter masks. Its working principle is to allow harmful air to pass through the filter material of the mask. After filtering, it is inhaled or exhaled.

  Here is a surgical mask. The standard surgical mask is divided into three 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 used to absorb the liquid and moisture released by the wearer. Surgical masks are suitable for basic protection of medical personnel or related personnel.

The composition of common surgical masks (Photo source:

  If worn properly, surgical masks can prevent droplets, sprays, or splashes containing large particles of viruses and bacteria from entering the mouth and nose. It also helps reduce your saliva and respiratory secretions from splashing on others, thereby preventing infection. However, by design, surgical masks cannot filter or block small (less than 5 microns) particles in the air, which may be spread by coughing, sneezing, or certain medical procedures. Because surgical masks and face stickers are loose and not tight, surgical masks cannot fully protect bacteria, viruses and other contaminants from entering the wearer’s mouth and nose.

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

  ②N95 mask

  The N95 mask is actually a respirator. The respirator is a respiratory protective device. Compared with ordinary masks, the design of the respirator fits the face more closely. It can filter particulates in the air very effectively. Among them, N means Not resistant to oil, which 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 level) test particles.

  If worn correctly, the N95’s filtering ability is better than the ordinary masks and medical masks mentioned above. However, even if it is fully compliant with the requirements, it cannot completely eliminate the risk of infection or death.

  To function effectively, we need to choose the N95 mask that suits our face shape. Before using it, check whether it is suitable, wear a respirator and adjust the rubber band, so that the respirator closely fits the face, but it is not uncomfortable. It is recommended to read the instructions carefully to see what different manufacturers have to say about “fitting well”.

  5. Are there any positive and negative sides of disposable masks? Will Dai Fang affect the prevention effect?

  The surgical mask is divided into three layers: inner, middle and outer. Ordinary disposable masks generally have two sides, the outer layer usually prevents liquid splashing, and the inner layer is a soft absorbent surface, so wearing it on the back will affect the effectiveness. You can check whether the wearing is correct according to the following methods:

  Touch: soft water-absorbing surface facing inwards, rough waterproof surface facing outwards;

  Nose bridge metal edge: the exposed side of the metal faces outward, and the wrapped side faces in;

  Earhook thread: the thread of the general tailor is outside;

  Look at the color: generally white toward the inside, the colored part facing outward.

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

  N95 is divided into two types with or without exhalation valve. People with chronic respiratory disease, heart disease, or other diseases accompanied by symptoms of dyspnea may use the N95 respirator to make it harder for the wearer to breathe, so using the N95 mask with an exhalation valve can make them easier. And help reduce heat accumulation.

  The design of the exhalation valve is very delicate. There are several layers of flaps. During inhalation, the flap will close tightly to ensure that no particles enter. When exhaling, the flap will open, allowing the hot and humid air to escape. At the same time, there is a soft cover inside to ensure that no small particles enter.

  In the past two days, there have been many misunderstandings about the N95 with an exhalation valve. Some people think that the exhalation valve has no protection. A study published in 2008 specifically investigated whether the exhalation valve will affect the protection of the wearer. The conclusion is whether the exhalation valve does not affect the respiratory protection of the wearer. Simply put, the N95 with an exhalation valve can protect the wearer, but not the people around it. If you are a virus carrier, please choose N95 without exhalation valve, do not spread the virus. If you want to maintain a sterile environment, you can not use N95 with an exhalation valve, because the wearer may exhale bacteria or viruses.

  7. Is N95 disposable? Can it be reused?

  In fact, all N95 respirators are single-use, and it is impossible to determine the maximum number of safe repeated uses of N95 respirators under any circumstances. Whether it is safe to reuse N95 is affected by many factors (such as the risk of infection). However, under special circumstances, unless the product manual of the mask specifically emphasizes “only single use”, it can be considered for repeated use in daily use, but this approach is risky. The most obvious point is that the outside of the N95 has actually been contaminated, but users have not realized that there is a risk of infection after repeated use. If the conditions are limited, it is really necessary to reuse it, and you should pay attention to a few points:

  ① Confirm that 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, store the respirator separately to avoid contact with each other 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 dirty, or if you feel difficulty breathing after wearing it, you should remove it. The method of safely discarding the N95 is similar to a mask: put it in a plastic bag, then put it in a trash can, and wash your hands after handling.

  8. Is the protective ability of N95 masks the same as surgical masks?

  Studies have shown that there is no significant difference in the effectiveness of these two masks, which are several times different in price, against the infection of viruses.

  Previous studies in the laboratory environment have shown that N95 respirators can provide better protection against acute respiratory infections than surgical masks. But in a clinical setting, randomized controlled trials of N95 respirators have not shown the same benefits. However, it is too early to draw conclusions from the results of a single experiment, and the final conclusion needs to be further proved.

  A 2012 study found that a close-fitting face mask provides about 94% protection against airborne viruses, while a properly worn N95 respirator close to the face can provide greater than 99% optimal protection. But wearing any kind of mask loosely can only achieve 60% protection.

  Therefore, in theory, wearing the N95 correctly provides more comprehensive protection. But if N95 cannot be worn for various reasons, surgical masks are also a good choice.

  9. Can PM2.5 mask prevent virus infection?

  PM2.5 refers to particles with a diameter of 2.5 microns or less, and the expression “PM2.5 mask” is not rigorous, and different anti-haze masks should be analyzed in specific situations. For example, our commonly used 3M9001 and 3M9002 foldable anti-particulate masks with valves comply with the requirements of GB2626-2006 KN90, which means that it can block at least 90% (0.3 micron level) of the particulate test The test particles, although slightly inferior to N95, are much better than ordinary disposable masks. The 3M8210, which is recommended by more people, is in line with the KN95 standard itself, so it is possible to prevent viral infections.

Two foldable anti-particulate masks with valves (picture from the network)

  In general, if the “PM2.5 mask” in your opponent does not know how to deal with it, it is recommended to check its product specifications and then decide whether to use it.

  10. What should I do after the mask is used?

  If the mask is damaged or dirty, or if you have difficulty breathing through it, you should replace it with a new one. If you are in an infectious environment, please wrap it up and throw it away, or throw it in the trash bin in the hospital where infectious waste is handled, and wash your hands or disinfect immediately. Even if there is no infectious trouble, in order to protect yourself and others, it is recommended to put it in a plastic bag and then put it in a trash can. 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 does the mask expire? Because the ingredients of the mask will degrade over time, affecting its function. Over time, components such as straps and filter membranes of masks may age, which can affect the quality of the seal that matches the face. Depending on the type of respirator, filter media, other materials used, and date of manufacture, the expiration date will vary.

  Storage conditions are also a key factor affecting 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 where the respirator is stored should avoid contaminated areas, dust, direct sunlight, extreme temperature, excessive humidity and harmful chemicals.

  to sum up

  In terms of design, if ranked according to the priority of the wearer’s own protection ability (from high to low): N95 mask>surgical mask>general medical mask>general cotton mask.

Priority ranking of different masks on the wearer’s own protection capabilities

  If you are a virus carrier, please choose N95 without exhalation valve, do not spread the virus.

  Please purchase the N95 that is formally produced and meets the test standards! Beware of fakes!

  Masks are not a panacea, but wearing masks correctly and frequently washing and disinfecting can greatly reduce the chance of infection. You can choose the mask that suits you best according to your environment (probability of infection). Although the N95 has the best protection, it is not suitable for everyone. Many people feel very uncomfortable wearing N95, can not insist on wearing, in such cases, it is better to choose a surgical mask. Wearing a mask is better than not wearing it.

  Finally, reduce your travels and don’t go to crowded places! (Organized by Chen Tingyu)

  For reprinting, please contact the WeChat public account of the Academy of Sciences for authorization.

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