If you’ve ever worried about catching something from the air while flying or visiting a hospital, a new study may help you feel more at ease.
Scientists at Northwestern University have discovered that the air inside airplanes and hospitals mostly contains harmless microbes—mainly the kind found on human skin.
The research, published in the journal Microbiome, is the first of its kind. Researchers used an unexpected method to study the air: they collected used face masks and an airplane air filter to examine which bacteria were floating in these enclosed spaces.
Their findings showed that most of the microbes in both settings are not dangerous and are the same kinds we encounter in everyday indoor air.
In total, the scientists found 407 different microbial species across all their samples. Most were harmless skin bacteria or microbes from the general environment. Although a few potentially harmful bacteria showed up, they were found in very small amounts and didn’t show signs of causing illness.
The study not only reveals what kind of bacteria are in shared air but also shows how face masks and air filters can serve a second purpose—as useful tools to monitor air quality in crowded places.
The project began in early 2022 during the COVID-19 pandemic, when people were especially concerned about catching viruses on airplanes. Lead researcher Erica Hartmann, an expert in indoor microbiomes, first planned to study the high-efficiency air filters used in airplane cabins.
These filters, called HEPA filters, can trap tiny particles very effectively, making them a great source for air sampling.
But there was a problem. These airplane filters are expensive and hard to remove. Taking them out for testing required grounding planes for maintenance, which was costly and complicated. So Hartmann and her team looked for a cheaper, easier option: used face masks.
They asked travelers to wear face masks during flights—both domestic and international—and send the used masks back in sealed bags. To compare different settings, they also collected masks from hospital workers who wore them during their shifts. Some masks that were taken on flights but never worn were also tested as controls.
When the researchers examined the DNA collected from the outside of the masks, they found something surprising: the air in hospitals and airplanes looked very similar in terms of the types of microbes floating around.
Most of the bacteria came from people’s skin, not from illnesses. The results suggest that people are the main source of airborne microbes in these settings, not the buildings themselves.
The team also found a few genes that are linked to antibiotic resistance, though they didn’t point to specific dangerous bacteria. These genes show how widespread resistance has become, but they weren’t found in high levels.
This study should reassure people who are nervous about air quality in public places like hospitals and airplanes. However, the researchers reminded everyone that germs don’t only spread through the air. Touching shared surfaces or coming into close contact with someone who is sick are still major ways diseases spread.
Even though the air is mostly harmless, Hartmann says, washing your hands remains one of the best ways to stay healthy.
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