Spacecraft may need to be dirtier to keep astronauts healthy

There may be logic in keeping spacecraft as sterile as possible, but this could inadvertently be affecting astronauts’ health

By Michael Le Page

27 February 2025

The International Space Station may be a bit too clean

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The strategy of keeping spacecraft as clean and sterile as possible to ensure astronauts don’t become ill may be a mistake. Our immune systems may need stimulation from certain kinds of molecules and microbes to stay healthy, say researchers who have been studying the International Space Station (ISS).

“The general notion is to try to have as few microbes as possible, but the question is if that is the best thing to do for long-term space travel,” says Pieter Dorrestein at the University of California San Diego. “And it’s also relevant for places on Earth, such as research [stations], hospitals and submarines, where you can spend months or more.”

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One reason for sterilising spacecraft is to avoid contaminating planets, such as Mars, with microbes from Earth, but the main concern is that an infection that would be easily treatable on our planet could become a major issue on a spacecraft.

Dorrestein and his team have analysed more than 700 swabs of surfaces onboard the ISS, and found it is indeed squeaky clean in terms of the diversity of the molecules and microbes present.

“The space station is just devoid of a lot of molecules and microbes,” he says. “It is at the extreme end of human living.”