Astronauts often experience immune dysfunction, skin rashes, and other inflammatory conditions while traveling in space. A new study suggests that these issues could be due to the excessively sterile nature of spacecraft. The study showed that the International Space Station (ISS) has a much lower diversity of microbes compared to human-built environments on Earth, and 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 in the space station.