Save the masks, and save yourself

About wearing masks

One of the key features of the COVID-19 visuals is people wearing masks.

There are plenty of recommendations, and authoritative ones too, for the average person on wearing or not wearing masks.

It looks like out of all the apparently contradicting information there is a common denominator: basic masks do not offer a secure protection to the average person from exposure to the virus causing COVID-19 pandemic.

That said, the majority of recommendations, not to mention the behaviour of about 1.4 billion people in China and the effect achieved there, stand for the opportunity to wear masks.

The explanation of the apparent contradiction is easy: face masks may not secure each individual in the public from possible exposure to the virus, but would definitely protect the public from intense spreading of the virus from those who are infected and may not know. Moreover, masks interfere effectively with the possibility to touch mouth and nose with hands that might have been in contact with surfaces loaded with the virus.

To complete the explanation there is another relevant fact, that might not be completely clear to many people: COVID-19 develops from exposure to a specific virus, like many other viral diseases.  In order for a viral infection to establish and develop to a level that can be detected and become symptomatic, it is necessary that enough viral particles have access to the receptive tissues in the body. The immune system start reacting to any amount of virus particles but only when the reaction reaches a certain level then the body develops easily detectable symptoms.

Severity of symptoms, as well as prognoses, depend on a combination of factors: individual characteristics such as set of genes and physical structure, specific conditions such as stress, age, and pre-existing diseases, but also amount of virus particles one is exposed to in the beginning and again over time.

A tiny exposure may trigger immune reaction at a level that is not detectable, but that fosters a certain level of immunity while a large and repeated exposure would cause symptoms and possibly worsen them. The large clusters developing in hospitals and community gatherings and the severity of symptoms detected in relation to those situations could be easily explained this way.

With this explanation it seems clear that every single tiny bit of protection of self and of those around us is of crucial importance and may make the difference within life and death for many, whether that’s the elderly in general, our parents, our siblings suffering depression, or even ourself.

Masks are a relevant component of that double sided protection, but their patchy availability makes the recommendation to use or not use them very dependent on priorities. Medical staff needs them to provide medical care, they need to protect self as much and as long as they can, and they need to avoid cross infecting patients. People staying at home do not need them, unless they are already infected and may infect or reinfect each other.

But also people at home need supplies and may need to move in places where spreading is possible. For this reason, availability and best use of available masks is crucial.

To recap:

  • Use masks when outside and in the presence of others apart co-living family members.
  • Masks offer a limited, but important protection.
  • You need masks to protect others not only yourself, do not use masks with a valve because those do not protect others!
  • Leave masks that offer high protection to those in real need, such as hospital and healthcare professionals, and use for yourself the next best option.
  • If you do not have masks, then do all you can to avoid getting in places and situations where you should wear one.
  • If you have a limited supply of masks, then learn how to reuse and recycle them.

This introduces the concept of reusing and recycling masks.

Reusing means simply take the mask off after use and wear it again when you need it. You should not do this when you don’t have the means to properly clean your hands and your face and you don’t have a place to properly keep the used mask. The moment you remove the mask is when your hands get closer to your mouth, nose and eyes, which are the places where the virus can easily get hold of receptive tissues in your body. The mask can be differently contaminated on the outer and inner side, and you need to keep the two sides as separate as possible if you plan to reuse the mask. Fold it and put in the pocket does not seem like the right thing to do. Hang it on a balcony in full sunshine sounds more like it.


Recycling means to return the mask to its unused status after using and processing it to eliminate the possible contamination it might have accumulated.

The mask is a filter and all that is in the air and does not make it through will stay on the mask: Virus, bacteria, droplets from your breath, dust in the air and so on. As a filter, it has a limited capacity to collect pollutants and still allow passage of cleaned air.

The filter in the mask has very specific characteristics that make it effective. These characteristics are the result of a combination of factors such as the mechanical structure and the surface reactivity in terms of electrostatic properties.

These characteristics are the result of a very specific production process and their stability may be susceptible to factors such as presence of humidity, chemical compounds and elements, exposure to extreme temperature, mechanical stress. You don’t need to rip a mask into pieces to make it ineffective. Making it wet with water might be as detrimental too.

Different masks have different characteristics, and for each there might be a best option to extend the usability with especially suitable recycling cycles. Although one thing that is common to most of the masks available in commerce is that they accept extreme temperatures during transportation easily ranging from below zero to 70 degrees Celsius and more.

The virus causing COVID-19, fortunately, is extremely prone to deteriorate and be destroyed by temperatures exceeding 50 degrees Celsius. This is also the case for a large range of other bacteria and viruses that may accumulate on a mask during use and pose an additional threat in case of reuse.

Also many biochemical compounds break down with temperatures in the range of 60 degrees, including some that may cause an unpleasant smell or clog the fibres of the filter.

The fortunate coincidence then is that pretty much every type of mask can be safely and effectively sanitized and partially restored by simple exposure to a temperature of 70 degrees Celsius for a limited amount of time, in the range of tens of minutes.

The recommendation then is to bake the masks for 30 minutes in an oven, possibly a ventilated oven at a constant temperature of 70 degrees. The masks should be put in the oven so that all parts of each mask are exposed to the hot air and not clumped together, keeping some part not exposed to the heat. Consider that the masks are made of a material that does not transmit heat, and therefore any part that is not exposed to the hot air may never reach a high enough temperature to secure sanitation.

After baking the mask you should preserve them in a dry and clean place. Consider that the masks have not been sterilized completely. Only the most crucial viruses, including the one causing COVID-19, and many bacteria have been destroyed or inactivated, but still there is a small population of resistant organisms that may cause as a minimum bad small, growth of mould, or even the development of bacterial colonies. Keeping the mask dry and clean takes out the elements necessary for the survivor micro organisms to thrive and become dangerous.

And for those who have no oven at home?

There are subordinate recommendations also based on the same concept of dry heating:

            1.         Close the masks in a zip sealed bag without pressing them together, zip-seal the bag, use a normal hairdryer and blow hot air on the bag uniformly for some 20 minutes avoiding to overheat and melt the plastic but assuring that every part of the bag has reached at least 70 degrees Celsius. Consider that plastic bag may start melting above 100 degree Celsius and the air inside the bag will be a little cooler than the air the hairdryer blows. A plastic bag full of air at 70 degrees Celsius feels definitely hot, but not as hot as not to be able and hold it.
Why you need a bag and cannot simply blow with the hairdryer?
I presume you are not trying to blow viruses all over the room, are you? You contain all the contaminated matter within the bag until it has all been exposed for long enough at high enough temperature.

            2.         Put the masks in a black metal box contained in a much larger sealed transparent plastic bag, big enough to contain the box without touching its surface apart from the bottom. Place the box with the bag directly under the sunshine until it becomes hot. You may open now and then the bag and measure the temperature of the box with a thermometer. If you don’t have a thermometer, consider that ethanol (common alcohol)  boils at 78.24 degrees Celsius and other alcohol commonly used in the household (methanol) boils at 64.5 degrees. A drop of them should boil out on the surface of the box.

            3.         Put the masks in a zip sealed bag, boil a large pot of water keeping the level of water at about 2/3 so that it is possible to put the bag in the pot once the water boils. As soon as the water boils turn off the heating of the pot, put the bag containing the masks in the water and cover the pot with the lid. When the water is cold again take the bag out, wipe it dry, open it and take out the masks sterilized.

All the procedures are better performed monitoring the process with a decent thermometer, like the ones used to stick in a roast while baking that can stand oven temperature. A thermometer in contact with the masks measures the temperature of the air surrounding the masks and gives a very good indication of the heating profile. Once you have fine-tuned the process, then you can easily repeat it using the same parameters.

How many times can you recycle masks?

There is no specific recommendation. The effectiveness of the mask over time and heating cycles depends on its intrinsic characteristics, duration of use between recycling cycles, other factors such as contamination with other pollutants, humidity, concentration of dust in the air, etc.

Considering a use of about one hour every day, consistent with procuring supplies for a household, and a stock of 10 masks, it is proper to estimate a period of about 2 months with 6 recycling cycles.

If the mask is to be used for 8 hours at work and possibly another 2 hours commuting, then the person using it should be working in an essential job and thus should be provided with a sufficient supply of masks to change at least 2 every day and dispose of the used ones.

Why not using water, soap, steam, alcohol, UV, ozone to sterilize the masks?

There are many technical reasons to answer the question, and for every type of mask the answers may vary. But there is a very simple way to answer it: what are the conditions of use of the mask and those that the mask is designed to stand anyway at least during transportation? Hot, dry air.

In the same line of thought it is safe to consider that a moderate exposure to UV and Ozone should be safe for the mask, but might be not effective to sterilize it adequately. Both UV and Ozone although, may help improve the re-usability of the mask by breaking chemical compounds that may develop and accumulate causing bad smell.

This article is a preliminary exposition on which to base the design and construction of a simple and effective “mask recycler” based on the principle exposed.

A simple device to sanitise and recycle masks

A project is starting for an open source hardware product to be made available for DIY with largely available material as well as a DIY set and finished product.

References used for this article come from several sources and direct observation in China.

Some relevant information can be found here: – search engine specialized search selection on covid-19. – specific on mask reusing. – key study on oven heat cycle recycling. – opposing point of view. – extensive resource including link on reusing masks. – specific analysis on use and reuse of masks.

Leave a Response

Leave a Reply

Back to top