The Hidden Health Crisis in Space: Why the International Space Station Might Be Too Clean

The International Space Station (ISS) represents one of humanity’s greatest engineering achievements—a marvel of technology orbiting 250 miles above Earth. Yet, recent research reveals an unexpected challenge threatening astronaut health: the station’s extreme cleanliness. While sterility is crucial for preventing infections in a closed environment, scientists now argue that the ISS’s microbial landscape may be too sanitized, leading to immune dysfunction, skin conditions, and other health issues. This revelation has profound implications for long-duration space missions to the Moon, Mars, and beyond.

The Microbial Desert of the ISS

The ISS is a sealed, industrialized habitat where every surface is meticulously cleaned to prevent microbial contamination. Astronauts spend hours each week sanitizing handrails, computers, and ventilation systems with disinfectant wipes. However, a groundbreaking study published in Cell analyzed 803 surface samples from the station and found a startling lack of microbial diversity compared to Earth environments1719.

Key Findings:

1. Human-Dominated Microbiome: Over 90% of microbes on the ISS originate from human skin, gut, and oral cavities. The station lacks free-living environmental bacteria typically found in soil, water, or air on Earth613.
2. Chemical Overload: Disinfectants like quaternary ammonium compounds permeate the station, creating a chemical landscape that suppresses microbial growth while potentially fostering antibiotic-resistant strains1219.
3. Compartmentalized Communities: Microbial populations vary by module. Dining areas host food-associated bacteria, while hygiene zones contain fecal and urine-related microbes—patterns mirroring Earth hospitals but with far less diversity617.

This sterile environment contrasts sharply with Earth’s microbial-rich habitats, where humans coexist with trillions of bacteria, fungi, and viruses that train our immune systems and regulate bodily functions.

The Hygiene Hypothesis in Space

The hygiene hypothesis, first proposed in 1989, argues that limited exposure to microbes in early childhood increases susceptibility to allergies, asthma, and autoimmune disorders. On Earth, studies show that children raised on farms or in homes with pets develop more robust immune systems due to diverse microbial exposures316.

In space, astronauts face a similar problem: an immune system “stuck in idle.” Without environmental microbes to interact with, the body’s defenses become dysregulated. Research highlights several consequences:

• Immune Exhaustion: Microgravity and radiation already stress astronaut physiology. A 2023 study found that long-duration spaceflight reduces T-cell function and increases inflammatory markers like IL-1β and TNF-α, mimicking accelerated aging214.
• Skin and Gut Disorders: Over 60% of astronauts report persistent rashes or hypersensitivity reactions, likely linked to Staphylococcus dominance on ISS surfaces. Similarly, gut microbiome analyses reveal declines in beneficial bacteria like Lactobacillus and Faecalibacterium, which protect against intestinal inflammation1414.
• Mental Health Impacts: Isolation and monotony are well-documented stressors. Emerging evidence suggests that microbial deprivation may exacerbate mood disorders by altering gut-brain axis communication48.

“The ISS microbiome resembles a hospital isolation room—it’s effective for infection control but terrible for long-term health,” notes Dr. Pieter Dorrestein, co-author of the Cell study1219.

Lessons from Earth: How Dirt Could Save Astronauts

Terrestrial research offers solutions to rebalance the ISS microbiome. For example:

1. Probiotic Regimens

Probiotics like Lactobacillus casei and Bifidobacterium have shown promise in counteracting space-induced dysbiosis. A 2023 trial found that astronauts taking probiotic supplements experienced fewer gastrointestinal issues and stabilized immune markers4. However, probiotics alone cannot replicate the complexity of Earth’s ecosystems.

2. Space Gardening

The Veggie project on the ISS successfully grows leafy greens using hydroponic systems. Beyond nutrition, plants introduce environmental microbes and phytonutrients that could mitigate inflammation. A 2024 study found that astronauts who tended plants reported improved mental well-being, likely due to microbial interactions and sensory stimulation78. Future missions may incorporate soil-based systems to foster symbiotic bacteria-plant relationships1018.

3. Controlled Microbial Inoculation

Scientists propose introducing sterilized soil or fermented foods (e.g., kimchi, kombucha) to seed the ISS with harmless environmental microbes. This approach mirrors “rewilding” experiments in urban settings, where soil bacteria improve immune resilience1219.

Redesigning Space Habitats for Human Health

The ISS findings are a wake-up call for future missions. A Mars voyage, lasting over two years, demands habitats that support both physical and immunological health. Proposed innovations include:

• Bioactive Materials: Surfaces embedded with beneficial microbes or enzymes that break down waste while nurturing a diverse microbiome510.
• Modular Ecosystems: Separate zones for crew living, hydroponic farming, and microbial “greenhouses” to mimic Earth’s ecological interactions918.
• Personalized Monitoring: Wearable sensors to track astronaut microbiomes and immune markers in real time, enabling tailored probiotics or dietary adjustments14.

“We’re not suggesting astronauts live in filth,” clarifies Dr. Emmanuel Gonzalez, a microbiome researcher. “But strategic exposure to nature’s microbes could make spaceflight safer and more sustainable”117.

Conclusion: Embracing Complexity in Space

The ISS’s sterility paradox underscores a broader truth: human health relies on microbial partnerships forged over millennia. As we venture deeper into space, engineers must shift from purely defensive strategies to ecological design—integrating microbes as allies rather than adversaries.

Future habitats on the Moon or Mars could blend cutting-edge technology with ancient wisdom, creating environments where astronauts, plants, and microbes thrive together. After all, if we’re to become a multi-planetary species, we’ll need to bring a piece of Earth’s vibrant ecosystem with us.

1. NASA GeneLab Study on Astronaut Gut Microbiome (2024)
2. PMC Study on Microgravity and Immune Dysfunction (2023)
3. Vox Article on the Hygiene Hypothesis (2014)
4. PMC Study on Probiotics in Space (2023)
5. ASM Article on Microbes in Space (2022)
6. Technology Networks Article on ISS Microbiome (2025)
7. NASA Article on Space Gardening (2023)
8. NASA Study on Gardening and Mental Health (2024)
9. NASA Plant Habitat-06 Investigation (2023)
10. PubMed Study on Microbial Ecology in Space Agriculture (2006)
11. CMM Online Article on ISS Cleaning (2025)
12. Popular Science Article on ISS Sterility (2025)
13. Discover Magazine Article on ISS Microbiome (2025)
14. PMC Study on Long-Duration Missions (2019)
15. International Society of Microbiota (2025)
16. PMC Study on Hygiene Hypothesis (2006)
17. EurekAlert! Article on ISS Sterility (2025)
18. EarthSky Article on Space Gardening (2022)
19. Phys.org Article on ISS Microbial Solutions (2025)