Why having a dirtier space station is better for austronauts’ health

By Stephen Beech

The International Space Station is too clean and making it “dirtier” could improve astronauts' health, claims new research.

They often experience immune dysfunction, skin rashes, and other inflammatory conditions while traveling in space.

Now a new study, published in the journal Cell, suggests that such health issues could be due to the "excessively sterile" nature of spacecraft.

Researchers from the University of California, San Diego, found that the International Space Station (ISS) has a much lower diversity of microbes compared to man-made environments on Earth.

The microbes that are present are mostly species carried by humans onto the ISS, suggesting that the presence of more microbes from nature could help improve human health on board.

Study co-first author Dr. Rodolfo Salido said: “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."

The research team worked 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 team identified which bacterial species and chemicals were present in each sample.

They then created three-dimensional maps illustrating where each was found on the ISS and how the bacteria and chemicals might be interacting.

The researchers found that, overall, human skin was the main source of microbes throughout the ISS.

Chemicals from cleaning products and disinfectants were present throughout the station.

The team also found that different “modules” or rooms within the ISS hosted different microbial communities and chemical signatures, and the differences were determined by the module’s use.

For instance, dining and food preparation areas contained more food-associated microbes, while the space toilet contained more urine- and poo-related microbes and metabolites.

Study co-first author Dr. Nina Zhao said: “We noticed that the abundance of disinfectant on the surface of the International Space Station is highly correlated with the microbiome diversity at different locations on the space station.”

When the researchers compared the ISS to different human-built environments on Earth, they found that the ISS microbial communities were less diverse than most of the samples from Earth.

They were also more similar to samples from industrialized, isolated environments, such as hospitals and closed habitats, and homes in urbanized areas.

Compared to most of the Earth samples, the ISS surfaces were lacking in free-living environmental microbes that are usually found in soil and water.

The research team says that intentionally incorporating these microbes and the substrates they live in into the ISS could improve the well-being of astronauts without sacrificing hygiene.

The team compares their suggestion to the well-studied beneficial impacts of gardening on the immune system.

Co-author Professor Rob Knight said: “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."

The research team hopes to refine their analysis to be able to detect potentially pathogenic microbes and signals of human health from environmental metabolites.

They say that those methods could also help improve the health of people living and working in similarly sterile environments on Earth.

Dr. Salido added: “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.

“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.”