The International Space Station (ISS) may be too clean for astronauts’ own good, according to recent findings suggesting that the station’s sterility enables hostile microbiota to flourish.
Immune dysfunctions, skin rashes, and various inflammatory conditions commonly plague spacefarers. A recent study found that the microbiota diversity on the ISS is significantly lower than in most environments on Earth, with those microbes present in space coming aboard with the astronauts.
Microbes on the International Space Station
“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,” said co-first author Rodolfo Salido of the University of California, San Diego.
Astronauts aided the researchers by swabbing 803 surfaces on the ISS, a 100-fold increase from earlier surveys. In an earthbound lab, the researchers identified the bacterial species and chemicals present in the samples. From these results, the team constructed three-dimensional maps of where bacteria and chemicals are present on the ISS, illustrating how they may be interacting.
While most health issues astronauts face have been minor, there are reasons to monitor the microbe communities aboard the ISS.
Health In Space
“Spaceflight conditions are known to weaken the immune system, increasing the risk of infections,” Salido told The Debrief. “Beyond human health, microbes also pose a risk to the spacecraft. Biofilms—microbial communities that form on surfaces—have been known to clog essential systems and even corrode spacecraft components, making microbial monitoring critical for both astronaut safety and spacecraft integrity.”
The risk associated with health complications increases in orbit, where access to routine medical care is unavailable. Easily treatable infections could have significant health repercussions under limited medical resources.
“Additionally, a sick astronaut could jeopardize mission success, especially during long-duration spaceflights where each crew member is responsible for critical tasks,” Salido added. “You don’t want a multi-year mission thrown off course because astronauts are battling a respiratory infection.”
International Space Station Microbes Identified
Human skin was the primary source of microbes, and cleaning products and disinfectants were also commonly found throughout the ISS samples. Intriguingly, different rooms called “modules” all had unique chemical signatures and microbial communities stemming from chamber use. Food-associated microbes were abundant in dining and food preparation areas, while urine and fecal microbes dominated toilet areas.
“We noticed that the abundance of disinfectant on the surface of the International Space Station is highly correlated with the microbiota diversity at different locations on the space station,” said co-first author Nina Zhao of UC San Diego.
Suggestions for Improving Health Aboard the International Space Station
The samples compared most similarly to hospitals, urban homes, and closed habitats on Earth, featuring less diverse microbial communities than normally expected on our planet. ISS surfaces lacked the free-living environmental microbes that generally make their homes in soil and water on Earth.
The researchers suggest cultivating these microbes by incorporating the substrates they live in on the ISS to improve astronauts’ health while maintaining hygiene. To do this, the researchers recommend bringing gardening to the ISS, a practice known to have significant positive health impacts for participants.
“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,” says Knight.
Next Step in Microbiota Research
The team’s next step is to refine their analyses to identify pathogenic microbes and appraise human health from metabolites. Innovations in these areas could also help people living and working in sterilized environments on Earth. A specific objective on that front is to advance monitoring technologies.
“One long-term goal is to develop methods for real-time, culture-independent microbial monitoring,” Salida said. “Right now, surface samples collected on the ISS must be sent back to Earth for analysis, which delays potential responses to microbial changes. If astronauts could analyze microbial communities onboard, they could make faster, more informed decisions about managing their environment.”
“These same monitoring technologies could also have applications on Earth, particularly in remote locations where laboratory testing is limited, such as deep-sea research stations, Antarctic bases, or hospitals where controlling microbial populations is critical,” Salida concluded.
The paper “The International Space Station Has a Unique and Extreme Microbial and Chemical Environment Driven by Use Patterns” appeared on February 27, 2025, in Cell.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.