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Masks - why you should still be wearing them

With the number of COVID cases continually dropping and regulations regarding masks long gone, we’re here to highlight why you should still be wearing a mask on the tube.

Masks, whether cloth ones or surgical masks, can provide protection from the heavy air pollution on the tube. PM2.5 concentrations on the tube are much higher than London overground environments and other subway networks globally (1). When covering your face, masks act as a protective layer which reduces your exposure to air pollution.

How effective they are depends on the type of mask you wear and how well it fits on your face. While cloth and surgical masks do provide some protection, they are not effective at reducing your exposure to fine pollution particles. Filtering facepiece respirators (FFRs) are designed specifically to reduce exposure to particles over 0.3 micrometres (µm), smaller than most of the air pollution particles on the tube. This means only a marginal amount of fine particles are seeping through the mask. Research has shown that some ultrafine particles (less than 0.1µm) can form into clusters between 0.3 and 2µm meaning FFR masks may protect against even smaller particles too (2).

How do they work? FFRs have multiple filter fabric layers, with electrostatically charged internal layers which ensure materials stick to them and cannot be inhaled. They also have a non-woven outer layer preventing larger particles from passing through. Fabrics and technology vary depending on brand, but FFRs have to pass many criteria to become certified respirators.

So how do you pick the right mask? There are different certifications globally and for Europe and the UK it is the FFP range. They come in 3 classes: FFP1, FFP2, and FFP3, having minimum filtration efficiencies of 80%, 94%, and 99% respectively (3). Buying FFP certified masks in the UK is recommended as they are:

  1. More readily available

  2. Less likely to be fake (poor quality and ineffective)

  3. Easier to breathe in than other standards

  4. Have a greater facial fit and therefore a lower rate of leakage of pollution (4, 5)

FFP1 masks are not recommended due to the low filter rate, while FFP3 masks are more expensive and may not be best for everyday use. FFP2 masks provide a great balance of comfort, breathability, protection, and reusability. Unlike the FFP3 masks, reusable versions of the mask are readily available and so FFP2 masks offer a more cost-effective solution to tube pollution. Some masks have a valve to help with breathing (while not compromising filtering) while others have materials fit for sensitive skin, so be sure to find the perfect option for you!

Key tips:

  1. Buy from trusted brands and websites*

  2. A snug facial fit is essential (6)

  3. Children absolutely require smaller masks

  4. Filter efficiency drops after time and with washing, so follow given guidelines

  5. Limit time wearing FFP2 masks to 75 minutes, with a 30-minute break afterwards (7)

*While we are yet to have specific recommended brands, sites such as the Respirator Shop, the Face Mask Store, and Protective Masks Direct provide a range of brands and models. We are working to find masks within the UK that are certifiably effective and lasting.


1) Smith, J. D., Barratt, B. M., Fuller, G. W., Kelly, F. J., Loxham, M., Nicolosi, E., Priestman, M., Tremper, A. H., & Green, D. C. (2020). PM2.5 on the London Underground. Environment international, 134, pg.105188.

2) Sheikh, H. A., Tung, P. Y., Ringe, E. (2022). Magnetic and microscopic investigation of airborne iron oxide nanoparticles in the London Underground. Sci Rep 12, pg.20298.

3) Lee, S. A., Hwang, D. C., Li, H. Y., Tsai, C. F., Chen, C. W., & Chen, J. K. (2016). Particle Size-Selective Assessment of Protection of European Standard FFP Respirators and Surgical Masks against Particles-Tested with Human Subjects. Journal of healthcare engineering, pg.8572493.

4) Myr, S. R. (2014). My personal fit testing: Here’s the best and worst pollution mask for me. MyHealth Beijing.

5) 3M. (2020). Comparison of P2, FFP2, KN95, and N95 and Other Filtering Facepiece Respirator Classes.

6) Cherrie, J. W., Apsley, A., Cowie, H., Steinle, S., Mueller, W., Lin, C., Horwell, C. J., Sleeuwenhoek, A., & Loh, M. (2018). Effectiveness of face masks used to protect Beijing residents against particulate air pollution. Occupational and environmental medicine, 75(6), pg.446–452.

7) Kisielinski, K., Giboni, P., Prescher, A., Klosterhalfen, B., Graessel, D., Funken, S., Kempski, O., & Hirsch, O. (2021). Is a Mask That Covers the Mouth and Nose Free from Undesirable Side Effects in Everyday Use and Free of Potential Hazards?. International journal of environmental research and public health, 18(8), pg.4344.

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