The hidden risk of space travel: How a sterile ISS might be making astronauts sick. Astronauts on the International Space Station (ISS) face many well-documented challenges: weightlessness, isolation, and the psychological strain of being far from Earth.

But new research suggests that the ultra-sterile environment of the ISS may also be compromising their immune systems—potentially increasing their risk of rashes, infections, and other health problems.

A team of U.S. researchers has created the first-ever 3D map of microbes on the ISS, revealing an “extreme” lack of microbial diversity. Their findings, published in Cell, suggest that astronauts are living in an environment comparable to a hospital—one that may be making them more susceptible to illness.

Why Does Microbial Diversity Matter?

On Earth, we’re constantly exposed to a vast array of bacteria, viruses, and fungi. These microbes are essential for a healthy immune system, helping our bodies fight infections and maintain balance.

However, the ISS operates in a closed-loop ecosystem, meaning astronauts are exposed to only a small subset of microbes—mostly those brought up by previous crew members. According to Professor Rob Knight, a computational microbiologist at the University of California, San Diego, the ISS has an unusually low diversity of microbes, with an overrepresentation of bacteria related to human activity.

This lack of microbial diversity has been linked to weakened immune responses in astronauts. Similar patterns have been observed in hospital environments, where excessive sterilization can lead to an increase in antibiotic-resistant bacteria and immune-related illnesses.

Mapping the Microbial Landscape of the ISS

To better understand the microbial ecosystem on the ISS, researchers sampled 803 surfaces across nine key compartments, including:

  • The airlock
  • Laboratory spaces
  • Sleeping quarters
  • Food preparation areas
  • Bathroom facilities (Tranquility Node)

The study produced a dataset 100 times larger than any previous microbiological study of the ISS.

Among the key findings:

  • Microbes related to food were most concentrated in the galley.
  • Fecal microbes were found primarily in the bathroom area.
  • Cleaning chemicals were detected in high concentrations, especially in the Tranquility Node, indicating frequent sterilization.

Interestingly, before the study, astronauts were asked to stop disinfecting surfaces for four days to allow for more accurate sampling. Despite this, high levels of cleaning compounds were still detected, suggesting that the ISS is being kept in a near-constant sterile state.

How This Affects Astronauts

For years, space agencies have observed that astronauts experience increased rates of rashes, cold sores, and infections while on the ISS. These symptoms persist even after they return to Earth, with astronauts needing up to a month to fully regain their immune strength.

Professor Knight suggests that the ISS’s microbial imbalance may be contributing to these health issues. Previous studies have shown that environments with low microbial diversity—such as hospitals and ultra-clean homes—are linked to weakened immune function and increased susceptibility to certain illnesses.

This could be particularly concerning for future long-term space missions. While today’s astronauts spend only a few months at a time on the ISS before returning to Earth’s microbe-rich environment, those traveling to Mars or living on Moon bases will spend years in these sterile conditions.

According to Professor Ashley Franks, a microbiologist at La Trobe University, this situation can be compared to a “hyper-office”—similar to the conditions found on long-haul flights, where people are trapped in a confined space with limited microbial input. “If you do get a build-up of antimicrobial resistance, it could more easily infect someone, and then you can’t treat them,” Professor Franks warned.

Can We Reintroduce Microbes to the ISS?

If the problem is too few microbes, why not just introduce new ones? Unfortunately, the solution isn’t that simple. The ISS is a delicate environment, and introducing new microbes carries risks.

On Earth, microbial ecosystems have had millions of years to evolve and reach a balance. In space, a newly introduced microbe could spread uncontrollably, potentially damaging equipment or posing health risks to astronauts.

“You don’t want microbes growing through your computers or anything like that,” Professor Franks explained.

A Potential Solution: Animals in Space?

One unconventional idea proposed by scientists is to introduce pets or small animals to help maintain microbial diversity. Studies on Earth have shown that households with pets tend to have a healthier and more diverse microbiome than those without.

“Just take a dog with you next time to the space station,” Professor Franks joked.

While pets on the ISS may not be a viable option, researchers are actively exploring controlled ways to reintroduce beneficial microbes—both for astronaut health and for supporting plant growth on long-term space missions.

The Future of Microbial Research in Space

This study represents a major step forward in understanding the microbial environment of the ISS. With the upcoming Artemis Moon missions and planned Mars expeditions, solving the microbe dilemma will be critical for ensuring astronaut health on long-duration missions.

Researchers are now working on ways to artificially introduce and regulate beneficial microbes in enclosed environments like space stations, submarines, and future space colonies. If successful, these efforts could revolutionize space travel—ensuring that astronauts stay healthier as humanity ventures deeper into the cosmos.

You also might be interested