Results of a new study led by Dr. Richard Peltier of the University of Massachusetts Amherst School of Public Health and Health Sciences suggest inexpensive cloth masks worn by people who hope to reduce their exposure to air pollution vary widely in effectiveness and could be giving users a false sense of security, especially in highly polluted areas.
[Photo: A selection of masks tested in the study]
Dr. Peltier, postdoctoral associate Dr. Kabindra Shakya, and their colleagues believe theirs is the first study to rigorously test disposable surgical masks and washable cloth masks, which are widely used in Asia and Southeast Asia. Their study shows “wearing cloth masks reduced the exposure to some extent,” but “the most commonly used cloth mask products perform poorly when compared to alternative options available on the market.”
Dr. Peltier says users should not assume such masks convey protection, “especially if an individual makes personal choices not to avoid high concentration environments because they assume they are protected from these contaminants.” Study details appear in the current Journal of Exposure Science and Environmental Epidemiology.
It was during an earlier air quality research project in Kathmandu, Nepal, and other travel in Asia that Drs. Peltier and Shakya were struck by how many people wore surgical or reusable cloth masks on the street. Kathmandu has poor air quality because high polluting gasoline and diesel engines are common, as is burning tires and garbage.
“We found ourselves wondering how effective these masks are. I was shocked that we couldn’t find any research studies investigating them,” he says.
In a series of experiments with an experimental mannequin, the team tested four masks: one pleated surgical type, two cloth and one cone-shaped cloth with exhalation flaps. They tested for several variables and effectiveness in filtering out five different synthetic aerosol particle sizes plus three particle sizes of diluted whole diesel exhaust, which simulated real-world conditions. Among the cloth masks, the one with exhaust valves performed fairly well, removing 80-90 percent of synthetic particles and about 57 percent of diesel exhaust. Plain cloth masks were “only marginally beneficial” they say, in protecting people from particles smaller than 2.5 micrometers, often considered more harmful than larger particles because they can penetrate the lungs more deeply. They found that mask shape and ability to mold to the face boosted effectiveness. The cone-shaped cloth mask and snug-fitting surgical masks performed better than looser-fitting masks.
“Unfortunately, the least effective two mask types are also inexpensive, reusable and are widely used in developing countries, implying they are a popular consumer choice where pollution mitigation is warranted,” the authors note. Reusable cloth masks cost 10-15 cents and can be washed and worn for months.
Dr. Peltier says this study has implications well beyond Nepal, because these masks are very common in China and India, and across much of southeast and southwest Asia. “What became clear to us is that millions of people probably wear these masks and feel safer, but we worry that this is potentially making things worse, if they stand next to a diesel truck and think they are protected by the mask, for example,” he points out.