One might be tempted to believe that “one size fits all” applies to face masks, but most of us know that not to be true. And ill-fitting face masks can greatly increase the risk of both transmitting and contracting airborne diseases, as they allow aerosols to escape through the gaps in the face seal. In significant amounts. One study found that an unmodified medical face mask stops less than 42% of exhaled aerosols and less than 56% of cough aerosols. But a modified mask can block 99% and 95% of those same respective aerosols. So how can one get a good-fitting face mask? Engineers at the Massachusetts Institute of Technology (MIT) have developed a device for face masks that does the job nicely, laying out their research in a paper that was recently published in Nature Electronics.

Made to work with a range of commercially available face masks, MIT’s device sits on the interior side of a face mask and measures the contact between the wearer’s face and the mask. They’ve named the device a cMaSK — standing for conformable multimodal sensor face mask — and it’s got 17 proximity sensors embedded in a flexible polymer frame that sits around the edge of a mask. These sensors determine where the mask is touching skin at 17 different points. For an optimal fit, all 17 sensors should be touching the wearer’s face, and a Bluetooth-connected app tells the user where they need to make adjustments. The app, which is connected to a server that analyzes data with a machine-learning algorithm, also offers insights into movements and activities that could have impacts on the face mask’s fit.

But helping the mask wearer find a proper fit isn’t all this handy new device does; the cMaSK has additional sensors that measure temperature, humidity, and air pressure, which combine to detect activities such as coughing and speaking. The device also has the ability to measure vital signs, including breathing rate, while its accelerometer tracks the wearer’s movements. If you’re thinking that’s a lot of technology for a face-mask fitter, you’re right; the device was initially developed to gauge the effectiveness of mask-wearing in places with high levels of air pollution. Then the pandemic hit. We all started wearing face masks, and the research team saw a need for their device to have more widespread applications.

Researcher Jin-Hoon Kim says, “In this project, we wanted to monitor both biological and environmental conditions simultaneously, such as breathing pattern, skin temperature, human activities, temperature and humidity inside the face mask, and the position of the mask, including whether people are wearing it properly or not.” While face-mask fitting seems like the most practical use of the cMaSK right now, the team says they plan to focus their efforts on “populations such as children, elderly people, and societies with high levels of air pollution.” And not just with face masks, as they say their sensors could work for “other textile-oriented garments including bras and t-shirts.” So one day, adjusting your undergarments could happen with just a few taps of an app.