Is the ISS Too Clean for Astronauts’ Health? New Study Finds the Space Station Lacks Microbial Diversity

Turns out, being too clean can be a bad thing. Scientists suggest the International Space Station (ISS) is so sterile that it may be making astronauts less healthy—and could even lead to problems like skin rashes, cold sores and immune dysfunction.

To better support astronauts’ immune systems, the team suggests intentionally cultivating communities of microbes in future space bases for humans. Their findings were published Thursday in the journal Cell.

“Sterile environments are not, in fact, the safest environments,” study senior author Rob Knight, a microbiologist at the University of California, San Diego (UCSD), tells Space.com’s Sharmila Kuthunur. “Exposure to beneficial microbes in the environment is important for maintaining health—this is not surprising, because as humans, we have co-evolved with those environmental microbes for millions of years.”

Researchers worked with astronauts to collect 803 surface swabs from the kitchen, bathroom, dining area and other parts of the ISS. They then analyzed the samples and compared them to buildings on Earth, including homes, hospitals and offices. This revealed that the space station lacks the microbial diversity that benefits human immune systems.

Microbes on the station were surprisingly uniform, and most were related to humans. It resembled areas on Earth that were industrialized or cut off from the natural environment. “The ‘home’ on Earth that looks most similar to the [ISS] was an isolation dormitory used during COVID 19,” says study co-lead author Haoqi Nina Zhao, an environmental chemist at UCSD, to Allison Parshall at Scientific American.

Human skin was the main source of most of the bacteria on the ISS, and importantly, the samples had very little of the microbes found in Earth’s soil and water.

“There’s a big difference between exposure to healthy soil from gardening versus stewing in our own filth, which is kind of what happens if we’re in a strictly enclosed environment with no ongoing input of those healthy sources of microbes from the outside,” Knight explains to Hannah Devlin at the Guardian.

The analysis also revealed high levels of chemicals from cleaning products used on the station, even though astronauts had been instructed to refrain from disinfecting surfaces for four days before collecting samples.

Scientists don’t know for sure how much the absence of microbial diversity is affecting astronauts’ health. But “[a lack of] microbial diversity in other environments, such as homes, has been associated with health problems parallel to those seen in astronauts,” Knight says to Jacinta Bowler at the Australian Broadcasting Corporation.

The study’s findings can help provide insight into which kinds of bacteria could be added to space habitats. “Future built environments, including space stations, could benefit from intentionally fostering diverse microbial communities that better mimic the natural microbial exposures experienced on Earth, rather than relying on highly sanitized spaces,” says Rodolfo Salido, a researcher at UCSD and co-lead author of the paper, to the Guardian.

Still, scientists would have to test whether certain microbes might become dangerous in a space environment, even if they’re beneficial to human health on Earth, writes Space.com. Due to microgravity, radiation and physiological stress, immune systems have to work harder in space to overcome infections.

Odette Laneuville, a biologist at the University of Ottawa who was not involved in the study, tells the Guardian that she would exercise caution when introducing microbes from Earth to space. “I don’t want parasites and fungi up there,” she says.

Perhaps astronauts could bring more fermented foods to the space station, or introduce animals to it. Or, the team suggests, they could trade out chemical disinfectants for probiotic-based cleaners, which use harmless bacteria to outcompete the ones that might cause harm. “It’s not about avoiding being hygienic,” Salido says to Scientific American. It’s about learning to “include the microbial symbionts, or the microbial friends, that we evolved with.”