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

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."