There’s good data showing that masks (including surgical masks) really can stop pollution and even have demonstrated physiological benefits. Masks work. But one place data is lacking is for air pollution mask lifespan. Just how long do air pollution masks really last?
Really Just One Day?
I frequently run into people who suspect that the lifespan of masks is only one day. After all, these masks are disposable so surely they’re only designed to last one day? This person on Zhihu (and the 115 people who upvoted him) suspects you need to change your mask every day:
As does this person who sent me an email convinced that the lifespan of masks is no more than one day:
What Does 3M Say on mask lifespan?
Last year I had the chance to visit the 3M lab to test out the effectiveness of a bunch of different masks.
While I was there, I asked them how often I should change my mask for a new one. They wouldn’t give an answer.
Why? I think they’re worried about giving a specific mask lifespan or timeframe to replace your mask, because many users are in industrial environments with super high or very toxic pollutants. So giving a general “you should change your mask after X days” answer could mislead people who work in completely different environments. But for folks like us in polluted cities like Beijing or Delhi who see a fairly “normal” range of pollution, we should be able to find a rough guideline.
Air Pollution Mask Lifespan: The Test
Fortunately, when I went to do fit tests, I had a 9332 mask that I had been reusing for 11 days. And when I say “used,” I mean “used intensely.” It was summer in Beijing, and I wore the mask while biking around town and sweating heavily. I estimate I used the mask at least four times every day for those 11 days. That’s a minimum 1.5 hours a day for 11 days, for a minimum total mask usage of 16.5 hours.
It’d be a lot better if we had lots of test data with more masks over more durations. But this data can at least test the popular conception that masks are single use (disposable) or one-day use only.
So what did the data say? Here are the results for a completely new 9332 mask (left) and my 11-day-old mask (right) showing how well it lasted.
98% after 11 days is pretty darn good! This contradicts the idea that you can only use these for a day or two.
So, How Long Do Masks Last?
The truth is, we need more data. With this limited data, my guess is that air pollution masks last at least two weeks. I use mine for 2-4 weeks, at which point the rubber bands break or they get really smelly and dirty! You can’t wash or clean masks (they’re made from the same material as HEPA filters – see our tests here), so the only thing to do when they get this gross is to throw them out.
Breathe safe–both inside and outside!
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Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.
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In terms of eliminating bacteria, would lightly spraying the surfaces with alcohol (inside and outside) help, or do you think it would ruin the fibre?
I’m no expert on this, however I know spraying will certainly help kill bacteria and viruses, but it will also likely damage the fibers. A light layer of alcohol that you then leave to dry naturally may help to kill bacteria whilst reduce damage to the mask. However, if you are still concerned then it’d be better to replace the mask altogether.
If changing the straps on this model, to a far more durable fabric-elastic material (used on other 3M models), they can be used in excess of a month. Try re-testing after a month or two. In conversation with 3M reps here in Taiwan, they’ve suggested that the filtration effectiveness increases over time, though the breatheability declines. There’s a logic there, as the membrane becomes infiltrated with particles, blocking transparency in either direction. Please do test again after 4-6 weeks.
You’re spot on David, just like HEPA filters, the filtration effectiveness of masks increases over time but at the same time the air resistance builds up which makes breathing more difficult. I’d still say the number one most important factor when considering when to change your mask is the breathability and dirtiness of the mask. After wearing a mask for 1-2 weeks, it often gets to the point where it’s smelly, sweaty and so not pleasant to wear. Again, just like HEPA filters, washing them will decrease their effectiveness, so there’s no easy way to clean them after they get… Read more »