Despite the fact that they are orbiting at an altitude of 250 miles above the Earth’s surface, daily life for astronauts aboard the International Space Station (ISS) sounds decidedly ordinary.

Just like the rest of us, they partake in three meals a day and aim to maintain a regular sleeping pattern.

They exercise for two hours a day, with special resistance and aerobic equipment to ensure that they don’t lose too much muscle mass while so far away from Earth’s gravitational pull.

In their recreation time they can enjoy whatever is practical up in space – including watching movies, taking photographs, reading, playing games, and of course, watching Earth go by from high above.

For the remainder of their time, like the rest of us, they’re working. As well as maintaining the ISS, an astronaut’s work during their average six month long mission there, is to collect valuable scientific data for interpretation back on Earth.

In order for all of this to take place smoothly, the ISS is kept very clean in order to protect the astronauts’ health. Without a medical center in convenient proximity, it’s important that these valuable scientists don’t become ill – especially not with anything contagious that could render the team out of action and even compromise the mission.

Of course, all crew members receive extensive medical training, with the designated Crew Medical Officer able to provide things like injections and stitches. And, if an astronaut became severely ill, contact with teams back on Earth may allow for missions to be adjusted so that the astronaut could be returned to Earth.

This is, of course, expensive and impractical.

As a result, rigorous hygiene practices – including the thorough and frequent use of disinfectant wipes – ensure that such an incident does not strike.

However, a recent study from scientists at the Centre for Microbiome Innovation at UC San Diego has discovered that this intense cleanliness may actually inhibit astronauts’ long-term health.

That’s because the conditions about the ISS are an artificial environment completely different from the microbe saturated world in which our bodies are designed to thrive.

In exploring the distribution of chemicals and microbes on board the ISS, the research team first created virtual models of the environment on board the ISS, with environmental surface samples from the United States Orbital Segment supporting their theories.

The data, which was recently published in the journal Cell, proved how few microbes proliferate the ISS. This study is ground-breaking for international space agencies, as Rob Knight, Faculty Director of the Centre for Microbiome Innovation, explained in a statement:

“For decades, space agencies worldwide have monitored the microbiome of the ISS, but this study provides an unprecedented, high-resolution, three-dimensional map of both microbial and chemical landscapes across the station’s interior surfaces. By covering nearly 100 times more sampled surfaces at a single time point than previous studies, this dataset offers an invaluable resource for understanding how space habitats shape microbial communities, and how these changes may impact both microbial life and astronaut health over time.”

And, in comparing their data to the microbes encountered by all of us during our everyday lives on Earth, the comparison was stark.

Though there was plenty of microbes on board the ISS – with the present microbes associated with the shedding of skin, sweat, and other debris from the humans aboard the spacecraft – the diversity of these microbes was much lower.

While this sounds like a good thing, it’s actually quite problematic, as the statement explains:

“The ISS has a much lower variety of microbes than almost any other environment, likely due to heavy cleaning and isolation—a lack of microbial diversity which could pose threats to astronauts’ immune systems. Additionally, microbial contributions from free-living terrestrial sources were minimal, suggesting astronauts lack environmental microbial exposures typical on Earth.”

While this is not such an issue in terms of a six-month mission to the ISS, if we were to board longer space flights – for example, the three years a trip to Mars would take – such immaculate attention to removing all traces of microbes could, actually, cause astronauts and passengers to become sicker.

Given the role that regular, low-level microbe exposure plays in maintaining a healthy immune system, the papers’ authors express concern about the long-term effects on astronauts health, with UC San Diego’s Rodolfo Salido Benítez making clear recommendations in the statement:

“Truly sterile environments—completely devoid of microbial life—are exceptionally rare on Earth. In space, excessive chemical decontamination may be counterproductive to maintaining a healthy ecosystem. By comparing the ISS to terrestrial habitats, our study highlights beneficial microbes that could be introduced to spacecraft as essential companions, supporting a resilient environment for long-term space habitation and exploration.”

And, beyond its relevance to space travel, the study could be extended to terrestrial environments too.

UC San Diego’s Pieter Dorrestein explained how, far from being alarmed by their potential to cause illness and disease, in our modern lives it is worth reconsidering the harsh obliteration of microbes:

“We often think about chemical exposures in terms of potential hazards, but this study challenges us to consider what we’re not exposed to. As urbanization and industrialization reshape our environments, we may be losing beneficial chemical interactions that once shaped human health. Understanding these missing exposures could help us create more balanced and supportive living spaces.”

Though no one is suggesting that astronauts should undergo too much in the way of microbial exposure – this would compromise our space missions for sure – the study’s recommendations are clear.

If our astronauts are to remain healthy on longer missions, their immune systems need a little something to grapple with.

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