How Many Times Can I Use a Mask?

Is it OK to use a respirator or mask many times or for a long period? These practices are used to reduce costs or when respirators and masks are scarce. They are sometimes called ‘extended use’.

For community use, we recommend extended use of N95s, FFP2, FFP3, CaN95s, CaN99s (respirators), and by extension, of disposable masks. This will also be relevant in health care settings where PPE is in short supply. Extended use will mitigate environmental concerns. More information on recycling and other methods of protecting the environment from these masks is needed.

For certified workplace protection, you should wear a respirator for which you have been fit tested; when fit testing is done quantitatively, this corresponds to >= 99% filtration in the inward direction, protecting the wearer. You should put on a respirator only once, and wear it for up to 8 hours, changing it if it is soiled inside (sneezing) or outside, or if you take it off to eat.

In other settings, using a harm-reduction model, it may be reasonable to use a respirator repeatedly, drying it out between uses. Discard it if the straps break or becomes visibly damaged or soiled, or if you don’t get a good seal with your user seal check.

The literature on extended use is sparse but encouraging. Extended-use respirators perform better than single-use medical masks, which typically provide protection of 50% (level 1) and 50-70% (level 3).

In Du, N95s used for 3 8-hour shifts still performed at 97%; after fourteen 8-hour shifts they were still above 80%.

In Degesys, there was increased fit failure the more hours, the more shifts, and the more donning and doffings; however, the repeat fit test (requires >99% filtration) used in this work is a very high standard; we don’t know by how much they failed because the methodology wasn’t quantitative. 

Bergman found that 52 - 75% of masks passed fit tests after 16 to 20 donnings and doffings, again a very high standard. All participants passed fit tests initially. N95s of 6 different designs were repeatedly donned. For the first 5 donnings, most continued to pass the fit test: for further donnings, the proportion passing the fit test fell.

Carsi studied FFP2s and surgical masks before and after 8- to 24-hour use, as flat materials, using particles in the 0.01 - 0.15 mcm range. They found that the filtration efficiency of the FFP2 but not that of the surgical mask was reduced by wear.

Chen studied fitted filtration efficiency of N95s, KN95s, medical and procedural masks and found them stable up to 40 hours.

Wang 2024a tested a variety of respirators worn by healthworkers in emergency departments, using the qualitative Bitrex fit test. The cumulative incidence of fit failure after one shift was 39%: categorized by respirator type, 26% in dome, 28% in duckbill and 61% in trifold. This corresponded to a hazard ratio 1.8 (95%CI 1.5 to 2.1): an 80% increase in the risk of failure for trifold compared with dome or duckbill respirators. After five shifts, the cumulative incidence of failure was 90%: 84% in dome, 86% in duckbill, and 95% in trifold. This study demonstrates that extended use does not provide regulated worker protection from airborne diseases.

Wang 2024b used quantitative methods, testing the 3M1860, 3M1870 and an unspecified Halyard respirator worn by healthworkers in emergency departments 2021-22. At the end of one shift, median and mean fitted filtration efficiency was 99% for all designs. After five shifts median fitted filtration efficiency was 97%, 96% and 92% respectively; mean fitted filtration was 96%, 96% and 90%. Though a large proportion of these respirators would have failed fit testing (>= 99% fitted filtration to pass) after even one shift, their filtration remains >90%. This is better than can be achieved with a new certified medical mask (50% level 1; 50-70% level 3).

Experts recommend that people have more than one mask, keep them in a paper bag with their name, date last worn, and the number of uses, written on the outside, and rotate the masks (one on, one off). Inspect the mask for physical soiling and breakage before re-donning. Minutes 2.27 to 5.0 of this video from the University of Nebraska Medical Center shows a paper towel and a paper bag version of how to store. 

A paper by Ong showed that it wasn’t possible to culture SARS-Cov2 from the surface of masks used by healthcare workers in brief contact (mean 6 mins) with patients with COVID is somewhat reassuring. The virus may be present, trapped in the mesh, but it doesn’t seem to dislodge easily. This study is limited by the brief exposure of the masks. 

The CDC in the US recommended extended use, for healthworkers requiring workplace protection against airborne diseases, in pandemic conditions only.

Extended use of medical and procedure masks should follow the same principles, though there are fewer data (Carsi).