The ISS is overly sterile: Making it 'dirtier' could improve astronaut health
by Cell Press
Astronauts often experience immune dysfunction, skin rashes, and other inflammatory conditions while traveling in space. A new study published in the journal Cell suggests that these issues could be due to the excessively sterile nature of spacecraft.
The study showed that the International Space Station (ISS) has a much lower diversity of microbes compared to human-built environments on Earth, primarily hosting species carried by humans onto the ISS. This suggests that the presence of more microbes from nature could help improve human health in the space station.
Discussion
"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 co-first author Rodolfo Salido of the University of California, San Diego (UC San Diego).
Methodology
The researchers collaborated with astronauts who swabbed 803 different surfaces on the ISS—around 100 times more samples than were taken in previous surveys. Back on Earth, the researchers identified which bacterial species and chemicals were present in each sample. Then, they created three-dimensional maps illustrating where each was found on the ISS and how the bacteria and chemicals might be interacting.
The team found that human skin was the main source of microbes throughout the ISS, with chemicals from cleaning products and disinfectants present ubiquitously throughout the station.
Microbial Diversity
When they compared the ISS to different human-built environments on Earth, the researchers found that the microbial communities on the ISS were less diverse than most Earth samples and more similar to samples from isolated environments, such as hospitals and homes in urbanized areas.
| Factors | Environmental Comparisons | Your Findings |
|---|---|---|
| ISS Microbial Communities | Less diversity | Similarity to sterile environments (like hospitals) |
| Earth Samples | Higher diversity | Presence of free-living environmental microbes |
The researchers related their findings to the well-studied beneficial effects of gardening on the immune system. "There's a big difference between exposure to healthy soil from gardening versus stewing in our own filth," says co-author Knight. "This suggests that we need ongoing input of healthy sources of microbes from the outside." This also aligns with suggestions from other fields of biology and environmental science.
Different ISS Modules and Microbial Communities
Distinct "modules" or rooms within the ISS hosted different microbial communities and chemical signatures, determined by their respective use. For example, dining areas contained food-associated microbes, while the space toilet was more likely to have urine- and fecal-associated microbes.
Interestingly, the abundance of disinfectant on the ISS surfaces was highly correlated with microbial diversity at different locations. This correlation suggests that reducing the sterilization protocols in favor of a balanced introduction of beneficial microbes could enhance astronaut health.
| Module Type | Microbial Communities Present |
|---|---|
| Dining Area | Food-related microbes |
| Space Toilet | Urine and fecal-associated microbes |
Implications for Future Space Missions
The researchers hope to refine their analyses to detect potentially pathogenic microbes and signals of human health from environmental metabolites. They argue that these methods could be expanded to improve the health of astronauts and other individuals living in sterile environments on Earth.
“If we really want life to thrive outside Earth, we can't just take a small branch of the tree of life and launch it into space and hope that it will work out,” says Salido. “We need to start thinking about what other beneficial companions we should be sending with these astronauts to help them develop ecosystems that will be sustainable and beneficial for all.”
Conclusion
This study highlights the potential benefits of integrating diverse microbial life into the ISS environment, not only to alleviate health issues experienced by astronauts but also to promote a more natural and supportive habitat for long-duration missions. Future strategies for habitation in space may benefit significantly from considering biological diversity akin to Earth’s ecosystems.
More information: The International Space Station Has a Unique and Extreme Microbial and Chemical Environment Driven by Use Patterns, Cell (2025). DOI: 10.1016/j.cell.2025.01.039
Journal information: Cell
