International Space Station is too clean – what does that tell us about how to co-exist with bugs on Earth?

York (UK): One of the cleanest places beyond Earth may be making its residents ill. Astronauts aboard the International Space Station (ISS) have had rashes, allergies and the odd infection, and scientists now believe the station’s environment is too clean. Researchers recently concluded that the ISS is so sterile it may be damaging astronauts’ health and have even suggested it might be time to make the station deliberately “dirtier”.

This might seem surprising. We’re constantly told to avoid germs, not embrace them. But the findings from space highlight a growing concern among scientists: that extreme cleanliness can sometimes do more harm than good.

The ISS lacks many of the environmental microbes, the sort found in soil, water and plants, that humans have evolved alongside for millennia. Instead, the microbial life floating around the station comes mainly from the astronauts themselves, such as bacteria shed from the skin.

In an environment sealed off from the natural world, the only microbes astronauts are exposed to are the ones they bring with them. Even though the crew stopped cleaning for a period before the study, scientists still found large amounts of chemical cleaning residues across the station’s surfaces.

The ISS is a microbial bubble: no fresh microbial input from outside and constant sterilisation from within. In such an environment, the immune system may struggle to function normally. That could help explain why astronauts commonly suffer immune-related issues like fungal infections, cold sores and unexplained skin conditions while in orbit.

For those of us back on Earth, this space station discovery offers a timely lesson. Modern life has given us a remarkable ability to control our surroundings. Homes are climate-controlled and filled with antibacterial sprays. Hand sanitisers are used regularly. Children’s toys, floors and worktops are scrubbed spotless.

But, as with all things, there may be a tipping point. Too much hygiene can interfere with how our bodies learn to defend themselves.

Our immune system isn’t just a shield against germs, it’s a complex network that needs training. From the moment we’re born, we begin learning how to respond to different microbes. Many of these are harmless and some are beneficial.

Early and repeated exposure to a broad range of microbes helps the immune system understand what is a genuine threat and what isn’t. Without that exposure, the system can overreact, triggering allergies, asthma and even autoimmune conditions.

There’s growing evidence for this idea. Children who grow up with pets or on farms, for example, tend to have lower rates of asthma and allergies. The thinking is that regular contact with soil, animal dander and a wider variety of bacteria helps build a more tolerant immune system. In contrast, children raised in more sterile, urban homes, with limited exposure to the microbial world, are more likely to develop allergic diseases.

Targeted hygiene

This isn’t a call to abandon cleanliness altogether. Handwashing, proper food hygiene and general sanitation have saved countless lives and remain essential. But there’s a difference between good hygiene and indiscriminate sterilisation. Not all microbes are enemies; many are part of our natural environment and play a key role in keeping us well.

One sensible approach is known as targeted hygiene. This means cleaning where it really matters, after using the toilet, before eating or preparing food, and when someone is ill while allowing more relaxed standards in lower-risk areas.

It might also mean accepting that a bit of outdoor mud, the presence of pets, or letting children get dirty now and then isn’t just harmless – it’s beneficial.

Some scientists are now exploring the idea of introducing friendly microbes into our homes and workplaces to restore microbial balance. There are cleaning products containing beneficial bacteria designed to crowd out harmful ones.

Other research is looking at how indoor environments, especially in places like hospitals, schools and public transport, could be made more microbially diverse without compromising safety.

Which brings us back to the ISS. If astronauts are becoming unwell due to a lack of microbial exposure, it may be time for space agencies to rethink their hyper-clean protocols.

The researchers behind the ISS study have proposed introducing safe, beneficial microbes into the station to replicate the sort of environmental exposure humans would naturally get on Earth. Future space missions may even incorporate microbial “gardens” or systems to reintroduce natural microbial communities.

Here on Earth, we don’t need to float in orbit to learn from this. The lesson is clear: balance is key. A world that is too dirty spreads disease. But a world that is too clean may leave us vulnerable in other ways.

The best defence may lie not in eradicating microbes entirely but in learning to live with the right ones. For astronauts and Earth dwellers alike, it may be time to welcome a little bit of good, clean dirt back into our lives.