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Disinfecting and Cleaning of Surgical Face Masks and N95 Respirators

N95 and surgical face masks can be disinfected and reused, but you must be careful how you disinfect them because they can be damaged if it is not done carefully.

However, cleaning, i.e., removing dirt and smell, without regard to viruses, is another matter which is far more challenging, as regards surgical face masks and N95 respirators. It is best to prevent them from getting dirty, such as having a disposable facial tissue between your face and the mask to absorb most of the moisture from your mouth and nose, and for ladies to keep makeup off the mask, which adds up to make it dirty and clog it.

Of course, a home made mask using ordinary fabrics such as cotton can be cleaned and disinfected however you want. However, surgical masks and N95 respirators have been made from a material which has been created with an electrostatic charge whereby chemicals can damage their filtration efficiency, and excessive heat can damage the material.

Health care workers who come into contact with many infected people should have their own guidelines, but other people who are exposed in public to many others, such as grocery store cashiers, post office employees, etc., and who have a shortage of surgical masks and N95 respirators, may decide whether or not to try disinfecting a mask, or how often to disinfect a mask. If they do want to disinfect a mask, then it becomes how best to do so in order to try to prevent degradation of the mask. Of course, the same applies to the general public who are not on the front lines.

Please keep in mind that a small dosage of viruses might not be enough to infect you, as there is a "minimum infective dose" of pathogens. However, we don't know what the minimum infective dose is for COVID-19. This topic of minimum infective dose is covered in another section on this website.

As regards cleaning a mask, the main issues are contamination and smell from your breath, and just dirtiness such as from air pollution. As of this time, no cleaning methods have shown promise yet. The best method, which I have practiced for a long time, is prevention, by just having a more abundantly available disposable mask placed in between your face and the mask, to absorb your breath. For example, you could choose a thin cotton materials which has little resistance to breathing, as is main purpose is just to absorb large particles of moisture, not the extremely tiny viruses and aerosols which the surgical mask or N95 respirator filters much more efficiently. Alternatively, just disposable facial tissue can also help a lot but may have a higher resistance to air flow.

Disinfecting a mask can help against growth of bacteria and other life on a mask. It won't remove it, but it might make the mask more tolerable to wear for much longer. (I've seen no research data on perfumes applied to masks. For example, many soaps have perfumes which don't contribute to cleaning or disinfecting but do make the soap more appealing, and give a "feel" of clean regardless of the efficiency of the soap.)

COVID-19 has been found to remain apparently active for days on surfaces, which includes virus trapped inside face masks or on them by touching with contaminated hands. Some people have suggested keeping a set of masks to just rotate, such as keeping 7 for a 7 day rotation, instead of trying to clean face masks, if you assume that the COVID-19 virus might not continue to be viable after 7 days in a minimal infective dose, but we actually don't know how long COVID-19 is viable, and it depends on just how much of it might be on a particular mask.

As noted later on this page, a practical way for home disinfection is putting a mask inside a common rice cooker set at "warm" but not "cook" with water at the bottom and the mask raised above the water such as in a steamer tray, and keeping it in this environment of high temperature and humidity for at least 30 minutes. For people who have a good oven, you can just set the temperature for 60C (140F) and put a wide pan of water inside to increase the humidity sufficiently. However, first let me explain:

Research on COVID-19 is still lacking, but various research has indicated that other coronaviruses and influenza viruses are damaged to make them ineffective, in an extremely high percentage, by heat of 60C (140F) combined with humidity of 50% or higher, applied for 30 minutes, though low humidity of 25% was judged insufficiently effective at damaging enough viruses.N95Decon-1

Testing some N95 face masks indicates that their capability to filter is not damaged much, if significantly at all, at temperatures up to at least 65C in moist heat, and at least 80C under dry heat, but the polypropylene filter starts to become damaged significantly somewhere between 80C and 100C as regards filtration capacity, in 1 cycle testing. At 60C and 80% humidity, two particular 3M masks retained >95% filtration efficiency after 5-10 cycles.N95Decon-1 As regards other things besides filtration, their elastic straps became damaged, but that is not an issue if they are mounted in a face mask sealer instead of using their own straps.

The above is based on reviews of multiple research reports, and it's recommended you follow those references for details. They also discuss alternative methods, such as peroxide vapor at room temperature, which is very good, but maybe not practical for people at home. Hospitals with mask shortages, may have their own more sophisticated methods for disinfecting large numbers of N95 respirators and surgical masks on more of an industrial scale.

Since surgical masks and N95 masks are very similar in their materials (with one of the differences being that N95 masks are designed to be sealed respirators instead of quick and easy loose fitting masks), I may believe that the above test results on N95 respirators may apply to the filtration capability of surgical masks, too.

However, what is clear enough is that for disinfecting by just heat and humidity, we need to be able to carefully control the environment to provide sufficient temperature and humidity -- not too much but not too little.

According to Wikipedia, rice cookers put on a "warm" (setting typically have a temperature of 65C (~150F)rice-cooker-wiki so that putting lots of water into a rice cooker and a raised steamer dish so that the surgical face mask or N95 respirator is not in the water but only in humidity could make for a reasonably good mask disinfection system at home in a practical way. Please be diligent to make sure it's on "warm" and not cooking, because cooking will raise the temperature to 100C (212F) or higher and probably damage the face mask. Also, I suggest you give it time to warm up before putting the mask inside, and give it a little bit more time.

Testing showed filtration dropping to ~80% after 100C for 10 minutes. There are many reports of damages around and a little bit above 100C, and melting around 160C.

Other reports state the same thing, that using soapy water, alcohol, and bleach immersion damages masks. N95Decon-2 One report found that immersion in medical alcohol at room temperature reduced the filtration efficiency of a medical mask from 93.2% to 67%.

A copy of two tables of data from testing are given at the bottom of this page. They may not be very easy for the general public to read, and my summary above may be sufficient for many people. The tables cover the temperatures and humidity need to disable viruses, and the damages or lack of damages to N95 masks in these temperature ranges.

Besides disinfection, what about just cleaning to remove ugly dirt and make the mask smell better?

For cleaning, one source reports that a surgical face mask which had a 93.2% filtration efficiency before cleaning, afterwards had just a 54% filtration efficiency after hand washing with soap for 2 minutes. If you're thinking of throwing away a mask because it's too smelly or dirty, you might want to think again, because 54% filtration is still comparable to many woven fabrics such as cottons, and a surgical mask or N95 respirator may still be easier to breath through for a given filtration efficiency. You may be able to wear 2 or 3 of them together to boost filtration efficiency up to 75% to 88%. If you clean using soap, it's best to minimize the mechanical stresses on the mask.

Research from Hong Kong tried washing with soap at a higher temperature of 60C (140F) and showed significantly different appearances under a microscopeHK-collab, though I did not see any measurements of theirs on resultant filtration efficiency. You can just go there to see their pictures online.

If you are temporarily discarding or storing used face masks, then I would recommend you store them in a paper container with lots of air inside but sufficiently sealed against dust, but not store them inside sealed plastic. This is because paper absorbs moisture, thereby reducing potential growth of mold and other things. After usage, there will be deposits from your breath in the mask. (I have worked with DNA samples, and this is why it is standard operating procedure to store them in paper, not plastic. In fact, samples we have received in sealed plastic were in many cases too damaged from fungus even though not old, whereas samples in paper over many months still produced good results.)

Alternative woven fabrics such as cotton of course can be disinfected and cleaned without being so careful, such as using soaps, higher heat, alcohol, and bleach. They just don't filter viruses as well, so the focus here is on disinfecting and cleaning much more sensitive materials such as surgical face masks and N95 respirators. As regards storage in paper bags, I'm talking only about surgical masks and N95 masks, which are much more effective in filtering viruses but more easily damaged.

I have seen other social media comments and website statements simply promoting disinfection and cleaning of surgical mask materials and N95 respirators in a positive way, without sufficiently discussing the issues. I may expect many people to Like and Share those positive articles... without bothering to take the time and effort to research the basis of any claims.

You should always clean and disinfect your hands before touching your mask anywhere.

Beyond masks, about cleaning and disinfecting options for surfaces such as door knobs, counters, tables, and other places where viruses from infected people may fall and then get onto your hands, there is considerable research on what works well to disable viruses, though not a whole lot regarding COVID-19 in particular.

The following is about disinfecting OTHER things, NOT surgical masks nor N95 respirators:

Scientific tests of different cleaning methods using the H1N1 influenza ("flu") virus have found that the most effective disinfectant is "quaternary ammonium chloride" (QAC) which you can find in many cleaners in grocery stores, but quaternary ammonium products may have other issues (see below). The second best results I've seen are with bleach, which may best be the chlorite kind of bleach. Alcohol was actually not as effective in some tests. Ethyl alcohol was usually chosen, at 70% concentration, mixed with water. The water also plays a role in disinfection in combination with alcohl. Isopropyl alcohol is apparently not as effective but better than nothing and still fairly good. Likewise, peroxide bleach was not as effective as chlorite bleach, but still worked fairly well.

All considered, ethyl alcohol or a good bleach may be preferable. Despite the better performance of QAC, an issue with quaternary ammonium is that tests of mice have shown reduced fertility after exposure. Even though you might have no plans to have any more children, any effects like that on the body may be enough of a concern.

Some of these can leave a strong smell on your hands.

It is important to wash your hands before and after touching a mask, as a primary means of transmission of viruses is by hands, such as touching door knobs after other people have coughed in their hand and also touched the door knob, and other such means. Touching your nose, eyes, and mouth with hands which have pathogens is a primary means of transmission. People have long established habits of touching their faces, and it has been commented that wearing a mask has probably prevented many infections because they habitually touch the mask instead of the face, but then the mask could become contaminated.

In some instances, I suggest using cheap disposable rubber gloves, or plastic gloves such as what food handlers wear. From my experience, rubber gloves are easier because you can still handle money easily and many other things, but they make my hands sweaty, and once you take them off they are usually inside-out and it's not easy to put them on again. Plastic gloves are loose and it's difficult to handle money with them on, but they can be taken off and put back on easily for re-use, such as when I want to use my mobile phone, and the glove can just be put into a back pocket.

I use gloves both outside to protect my hands from viruses in public, as well as at home when doing cleaning.

There are different kinds of quaternary ammonium and bleaches, so it may be important to choose a good kind of quat or bleach:

  • Many different kinds of disinfectants on the market use variations of quaternary ammonium ("quat"), but some tests used only the chloride (QAC) against influenza viruses.
  • Bleach types include chlorine (sodium chlorite or sodium hypochlorite), oxygen (hydrogen peroxide, or a compound which releases hydroxide such as sodium perborate or sodium percarbonate), and bleaching power (calcium hypochlorite). It was not always clear in studies which "bleach" worked best, but I lean towards the chlorites when available. (Sodium chlorite is NaClO2, and sodium hypochlorite is NaOCl or NaClO.) You can just read the ingredients on the package in the store, to see which type of bleach it is, e.g., look for chlorite.

Be very careful with bleach because if you drip some of it onto your clothes, it can create bright spots.

If you run out of alcohol, you can also use bleach to clean door knobs and other things, but be aware that it can cause corrosion. Alcohol is safer to many items than bleach.

Different sources have specified different concentrations of bleach, diluted with water, with a wide range, from no dilution to mainly water with a little bleach.

Do not ever mix bleach with other disinfectants or other things, as some of the potential chemical reactions can be dangerous. Bleach has been used routinely in households for a very long time for clothes whitening and other purposes, as well as in industry.

After finishing and putting the lid back onto the tupperware bath of bleach, I put the tupperware outside because it creates an odor inside the house. (I put it next to my front door, hoping to drive away mosquitoes, but I don't know whether or not it's effective at repelling many mosquitoes, if any.) Of course, if you put bleach into tupperware, then never use that tupperware again for storing food or drink, for safety reasons.

Bleach degrades over time, so don't stock up too much, and keep your stock in a cool place.

(There are various scientific research reports on disinfectants which are the basis for the above recommendations. Different studies have different results, and depend on the method used to detect the virus after cleaning. For example, a study compared a method used ("cell culture") which reported no virus found after cleaning, vs. a more sensitive detection method ("PCR") using the same cleaning method which found virus components on some of the same objects. It is quite possible that "cell culture" method may be more accurate, because PCR can easily detect components of viruses which have already been damaged and disabled in large numbers, but PCR is more sensitive, quicker, easier, and more economical.)

Again, don't use chemicals on N95 respirator filters nor surgical masks. Only heat up to around 65C and humidity over 50% should be applied, as discussed in the upper part of this page.

Virus damage and disinfection from heat and humidity

I have added the text in red, on top of the document from the original source.
Source: N95Decon Research DocumentN95Decon-1

N95 respirator face mask damage from heat disinfection

Source: N95Decon Research DocumentN95Decon-1

References and Footnotes:
Ref: HK-collab

Source: Hong Kong laboratory tests
The University of Hong Kong – Shenzhen Hospital
Department of Architecture and Civil Engineering, The City University of Hong Kong
Consumer Council of Hong Kong
Hong Kong Applied Science and Technology Research Institute (ASTRI)
Hong Kong Science and Technology Parks Corporation (HKSTP)

Ref: N95Decon-1

Source: Technical Report for Heat-Humidity-Based N95 Reuse Risk Management
Referenced by n95decon.org ... Thanks.

Ref: N95Decon-2

Source: Promising vs unsuitable methods at disinfecting
This is a summary about 3 good methods: humid heat, hydrogen peroxide vapor, and UV-C -- vs. damaging methods: soapy water, alcohol, and bleach immersion.

Ref: rice-cooker-wiki

Source: Rice cooker on Wikipedia

Ref: Tsai-Cai-elusive

Source: Cleaning a surgical or N95 face mask
Dr. Peter Tsai is a leading designer of air filters. He cites his colleague and their team, "Cai et al.", as having tested masks before and after hand washing with soap and water, and immersing in medical alcohol, in February 2020, but I have not found any original scientific report, and links have apparently been taken down or moved, so finding the original source has been elusive thus far, though this test result has been cited many times, including this MSN article which maybe will last longer. Somebody quotes him as saying "My colleague Dr. Cai, a retired filtration testing scientist, collected experimental data in February 2020, shown in the table below, that support my past results."

External links:

Alcohol and bleach as disinfectants (NCBI)

A scientific analysis of alcohol and bleach as disinfectants.

Effectiveness of Common Healthcare Disinfectants against H1N1 Influenza Virus on Reusable Elastomeric Respirators

in Infection Control and Hospital Epidemiology, Volume 35, Issue 07, July 2014, pp 894 - 897
Authors: Shobha S. Subhash, Maria Cavaiuolo, Lewis J. Radonovich, Jr, Aaron Eagan, Martin L. Lee, Sheldon Campbell and Richard A. Martinello

N95Decon collective on decontamination and reuse

N95Decon is a volunteer collective of scientists, doctors, other professionals, and students in academia, business, and elsewhere, for the purpose of recommending methods to decontaminate and reuse N95 filtration devices and other personal protective equipment (PPE), during this time of shortages during the COVID-19 epidemic.

For a directory of pages on this website, please see our SiteMap, where you might find some more things of interest.

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Parts of this website are derived from my pollution mask work in 2019.

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