 The immune system plays a critical role in protecting us from disease and infection. However, when exposed to prolonged periods of microgravity or radiation, the immune system can be compromised, leading to increased risk of illness and injury. Research has shown that these effects can be exacerbated by other factors such as alterations in metabolism, gut bacteria and oxidative stress. Future research must focus on understanding how these factors interact to create a comprehensive picture of the effects of space travel on the immune system. This article was authored by Pauline Jacob, Christian Ertlin, Bjorn Baselat and others.