Do masks really work in India’s air pollution?

Can air pollution masks help with India's air pollution?

Every year when winter rolls around, a billion people in India are left breathing toxic, polluted air when on the streets. Be it in Delhi, Mumbai, Kolkata or Hyderabad, everyone is forced to become experts in a complicated scientific question to cope with the pollution: Do air pollution masks work?

I’ve heard doubts from smart, skeptical people all across India on this question. There’s little real data out there showing whether pollution masks work, and even less information about the brands most commonly found in India. With the help of Smart Air nerd Dhariyash, who traveled down to a pollution mask lab in Mumbai, I’ll answer those doubts!


1. “There’s no way for pollution masks to capture the really small particles.”


The skeptic case: 

The most dangerous particles are the smallest particles, and levels of these are dangerously high across India. But masks are so thin! How could they possibly get those smallest particles?


The scientific pollution mask test:

Researchers from the University of Edinburgh tested different common masks by running a diesel generator (to mimic car exhaust) and piping the exhaust through different masks. They used a particle counter to see how many particles made it through the mask. This is a great benchmark for pollution in India, data shows that one of the main sources of air pollution is diesel generators (check out this report on Bangalore’s air pollution).

Here’s my super scientific rendering of the setup:



One important detail: the particle counter they used measures down to .007 microns. We’re talking about truly tiny particles here!

First, they tried a simple cotton scarf. Sometimes I see bikers in India wearing these.


can cotton handkerchiefs remove air pollution in India cities


Not great, 28% of particles blocked.

Next they tried a cheap surgical mask like the ones used in most of India’s hospitals:


surgical mask effectiveness at removing PM2.5 and air pollution


Surprisingly good! (Fit tests generally show lower results–see below–but still a lot higher than most people’s intuition.)

Next they tried several bike masks.


cycling masks in India removing air pollution PM2.5


Most were around 80%.

Then they tried several cheap 3M masks.



They all scored over 95%. Pretty good!

Conclusion: Masks capture even very small particles.


2. “OK, they capture the small particles, but when you wear them, all the air just leaks in the side.” 


The skeptic case: 

In theory, masks can catch the really small particles, but those tests aren’t on real faces! When you actually wear them, you can’t get a good enough fit, so they’re basically useless. What’s more, they’ve probably been made to fit foreign, not Indian faces!

The scientific test:

This question is tougher to answer because you have to measure the mask while you’re actually wearing it. For that, you need a really expensive fit test machine. Fortunately, I begged and begged a mask company in Mumbai until they let me use their lab.

We tested a whole range of common masks you can pick up in India – including some of the most expensive, the cheapest as well as the most common. They ranged from cotton surgical masks to N90 (equivalent FFP1), to N95 (equivalent FFP2) to N99 (equivalent FFP3). Here’s the setup and the masks we tested:

Common Indian masks including N95 (FFP2), N90 (FFP1) and N99 (FFP3)

And here’s how the machine works:

Dhariyash fit test air pollution mask Mumbai India


The blue tube is sampling air outside the mask, while the white tube is sampling air from inside the mask (more details on the methods here ). 

Smart Air India Head Dhariyash, along with two local kids from Mumbai who volunteered to take up the challenge of testing 20+ masks. This was great, because we were able to measure the results on Indian faces, as well as test various different kid’s masks with the help of our two young volunteers.

Kids air pollution mask fit test


Girl's kids mask air pollution effectiveness test

Here are the results of all the adult and kids’ masks we tested:


How well do masks work for the broader population? 

It’s important to make clear: masks that fit well on Dhariyash or the kids’ faces might not fit other people’s faces well. However, there is evidence from a broader population that masks fit most people well. A scientific study of 3M masks on 22 Chinese people found a median fit score of 99.5%–essentially the same as the top results from Dhariyash

So kids can wear masks too?

The Honeywell kids’ masks we tested had varying results. One mask fitted to Vijay (boy’s face) captured over 90% of PM2.5, however on the one fitted to Pallavi (girl’s face) didn’t do as well, capturing only 50% of the PM2.5 air pollution. This shows how important fit is for getting effective masks – the size and shape of your face will affect its seal.

Based on this data, and knowing that young children are much more sensitive to the impacts of air pollution, we decided to start offering these Honeywell Kid’s masks through our online store and Delhi-based office, to help more of India’s children breathe safe when outdoors.

But how about the price?

Best yet, effective masks don’t cost a lot of money.


India mask test cost and effectiveness


Based on these results, we’re now shipping the Venus N99 masks and the Honeywell Kids’ masks through our online store.

Exception: Gas Pollutants

Masks are great, but note that these are tests on particulate pollution (such as PM2.5). Most commercially available masks don’t target gas pollutants like NO2 and O3, so masks are not giving 100% protection.


3. Is there a documented health benefit of wearing a mask?

This is probably the hardest question to answer. However, there are two solid studies that have randomly assigned people in Beijing to wear masks or not and measured their heart rate and blood pressure (12).



While wearing masks, people had lower blood pressure and better-regulated heart rates.


We’re yet to see any tests like this done in Delhi or other cities in India, but we’re pretty certain the results would be the same.

Conclusion on pollution masks:

Masks capture even the smallest particles—even while people are wearing them (even Indians!) — and they have documented health benefits. That should be enough to satisfy even the skeptics!


The Sqair air purifier Kickstarter

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You should come to Mexico City

[…] pollution around their activity. Some startups offer nano-filters for embedding in the nose. N95 and N99 masks are also an option. Personal home or car air purifiers based on High-efficiency particulate […]


Hi Paddy – why cant I see the Venus N99 mask on the comparator graph for cost effectiveness? Thanks, Meenakshi

A question/ concern I’ve long had with the PortaCount testing protocol, is what impact does a real-world, moving, body-in-motion, environment have on the test. As compared to walking or cycling down a busy polluted street with outdoor air currents, testing a still body in an office room might or might not produce the same results. Hopefully we’ll see a testing system from PortaCount or other perhaps university research project, explore this matter. It may be quite needed. Uppermost in my mind are the millions of cyclists and motorbike riders using all variety of masks, assuming they have effective protection in… Read more »

Dhruv Kapur

Are these studies published in a reputed paper or journal? This will make these findings much more useful.