COVID: Can a surgical mask be used more than once?

During the COVID outbreak, you can reuse your surgical masks for yourself: between two uses, you just need to store your mask for a week in a paper envelope, while any coronaviruses that may be present on the mask are practically all inactivated.

Why reuse surgical masks?

• less pollution. These masks are made of plastic nanofibers. This plastic is not biodegradable and takes several hundred years to degrade. In all countries of the world, these masks can be found in garbage cans, streets and gardens, rivers and oceans. These masks are very ugly, dangerous for the animals that ingest them, and end up in the form of microplastics, a huge pollution whose dangers for the environment are still poorly known. If every person in France uses a single-use mask every day for a year, this creates about 100,000 tons of non-recyclable plastic waste in one year.
• less use of petroleum, necessary for the production of the polypropylene for the masks.
• less expenses: a box of 50 masks is enough for 2-3 people for one year.
• less out-of-country purchases: the majority of masks come from Asia.
• less risk of contamination from used masks, which are often thrown out outside.

Why is this reuse not officially recommended?
These surgical masks were designed in the 1960s for single use in a hospital environment under conditions of strict asepsis. Surgeons and nurses wear them to avoid contaminating the operating field, and not to infect the patient on the operating table with their saliva. The masks were sterile and were discarded after each operation.

It is with the COVID-19 pandemic (shortage of masks at the beginning, then massive consumption of surgical masks by the general public) that the issue of their recycling has become major. Nevertheless, governments and health authorities may fear the use of contaminated masks, and exchanges between users. In addition, manufacturers and retailers have an interest in selling as many masks as possible.

What is the evidence that this method is effective?
The method we propose is effective, but not absolutely: it does not clean dirty masks and does not sterilize them, and in case of massive contamination by coronavirus, some viruses may remain.

At room temperature, coronaviruses gradually lose their infecting power. On ordinary plastic this virus only survives for four days. On a mask experimentally contaminated with a high viral load, 99.9% to 99.99% of the coronaviruses SARS-CoV-2 are inactive after 7 days on the outside and 4 days on the inside. On the seventh day, between 0.01% and 0.1% of the starting viruses can still be extracted by washing the fibres.

We believe, however, that on a lightly contaminated mask there will be almost no virus left after 7 days, and that if any virus remains, it is strongly bound to the mask fibres by electrostatic attraction. Finally, the particles on the front of the mask cannot pass through it and therefore cannot be sucked in by the wearer of the mask. This reasoning is logical, and based on scientific data, but it does not guarantee the absolute effectiveness of the proposed method, which has never been rigorously tested with volunteers.

How can this be done in practice?
We are only talking here about the envelope method, which is the simplest and most practical. The members of our team have been using it for several months. For the other methods (dry heat, steam, disinfectant), see the question Can you reuse a mask?

• After use, simply store the mask in a paper envelope and wait a week before reusing it.
• Reuse only intact masks: no stains, holes nor tears, intact elastics, correct nose bridge.
• Wash your hands after storing the mask.
• Choose paper enveloppes instead of glossy paper envelopes (brown or plain white envelopes).
• Write the date onto the envelope, so as not to take it back too quickly, and keep a record of how many times each mask has been used.
• The envelopes can be re-used: after wearing the mask, it can be placed back in the same envelope.
• Make a stack of enveloppes by always placing the envelope of the last mask used under the stack, and using the decontaminated masks on top of the stack.
• Decontamination can be speeded up by exposing the envelopes and masks to temperatures above 25°C. The hotter it gets, the faster the virus is killed. On a radiator or in a black folder in the sun behind glass, if the temperature reaches 37°C, each day deactivates 99.9% of the virus. In an oven at 70°C, it will only take an hour.

Why storing masks in a paper envelope and not a plastic one?

• Paper decontaminates quickly. Within 30 minutes, 99% of the viruses have disappeared from the paper, and none remain after 3 hours. On plastic viruses persist for 4 days.
• The paper absorbs moisture and speeds up the drying of the mask.
• The rigidity of the envelope allows the mask to be smoothed out, preventing folds, fibre breakage and the appearance of small holes and tears.
• The paper is convenient for writing the date. Masks could also be hung on a hook or a coat hanger, but this would lose traceability and may result in a risk of contamination through contact.
• Storing the masks flat in a stack is convenient when running on more than seven masks. This is the case when using several masks per day.

How many times can you recycle your mask in this way?
The filtration power of surgical masks hardly changes after being worn (if they do not get wet), nor after being stored dry at room temperature because filtration is based on the mesh of the fibres and its electrostatic properties. After 30 uses, the loss of filtration and fit to the face makes the surgical mask comparable to a new fabric mask. Therefore, if one is careful, and the mask is not splashed, one can keep the mask for a very long time, and recycle it at least 20 or 30 times, allowing more than six months of use. Of course, you can choose to renew your masks more often.

Can you wash your surgical mask?
Yes, surgical masks can be washed and disinfected without losing their ability to filter 3 micron particles: after ten machine washes at 60°C with detergent and disinfectant, the filtration performance of 3 µm particles is very little affected, and it is the same after 5 wash+autoclave cycles. The breathability of the mask remains excellent, but the integrity of the elastics and the metal bar should be checked. However, the electrostatic charges of the polypropylene are lost after the first wash, which greatly reduces the retention of submicron particles. As aerosol droplets are generally between 0.5 and 1-5µm in size, the envelope method described above is preferable, as long as the mask is clean. That said, washing a surgical or FFP2 mask means swapping their effectiveness for that of a cloth mask (see the question Surgical mask or cloth mask: which to choose?). This will still filter out some of the aerosols, if not all, and therefore reduce the risk of contamination (see the question Does the severity of the disease COVID-19 depend on the dose of virus received?). Moreover, heating too much or for too long will damage the surgical mask, which is however resistant to 70°C for one hour.

Is this method as effective for FFP2/N95 masks?
Yes, the envelope method also works with FFP2 masks, especially the duck beaks that can be flattened into envelopes.

In conclusion, this efficient and economical method is simple enough to be used in practice for a long time. It is not risky, because the same person will always use the recycled masks, which cancels out the risk of transmitting germs other than coronaviruses. It is not ideal, since it does not guarantee total disinfection of the masks, but it is better than what many people do when they use their cloth masks as a cotton handkerchief: folded in the pocket, sometimes damp, taken out and put away many times without washing hands, and washed only when it is visibly too dirty to wear.

Warnings

• In cases where you think your mask may be heavily contaminated (intensive care unit, conversation with a patient or contact, large gatherings, visible soiling), it is best to discard the mask. Indeed, if the initial contamination is massive, the viral particles may not all be inactivated in 7 days.
• In cases where your mask has been wet, it should be dried carefully, either in open air or in a porous envelope (blotting paper), but not under the stack of enveloppes. In theory, a wet mask can allow the development of germs that are dangerous for an immunocompromised wearer (e.g. Aspergillus). After drying, the mask will have lost some of its filtering power, but it will still be more effective than a cloth mask.
• If you are particularly fragile or immunosuppressed, it is prudent to continue to discard your masks and use a new one each time. The same advice applies to caregivers who come into contact with these people.
• Don't share your masks with others. Everyone keeps their own germs to avoid contamination between people!
• Do not store the mask in the cold: the coronavirus can survive for a long time at 4°C, and even longer at -18°C in the freezer.
• If you have any doubts, throw away your surgical mask.