XUV flux evolution for Proxima and the Sun at the orbital distance of Proxima b and Earth, respectively. The two scenarios discussed in the text, namely a flat regime and a power-law decrease and a constant value throughout, are represented, with the gray area indicating a realistic possible range. Such relationships show that Proxima b has been irradiated at a level significantly higher than the Earth throughout most of their lifetimes and the integrated XUV dose is between 7 and 16 times higher, depending on the assumed XUV flux evolution for Proxima.