Metal halide perovskites (MHPs) are semiconductorswithpromising application in optoelectronic devices, particularly, in solar cell technologies. The chemical and electronic properties ofMHPs at thesurface and interfaces with adjacent layersdictatecharge transfer within stacked devicesand ultimately the efficiency of the latter. X-ray photoelectron spectroscopy is a powerful tool to characterizethese material properties. However, the X-ray radiation itself can potentially affect the MHP and thereforejeopardize the reliability of the obtained information. In this work, the effect of X-ray irradiation is assessed on Cs0.05 MA0.15 FA0.8 Pb(I0.85 Br0.15 )3 (MA forCH3 NH3 , and FA forCH2 (NH2 )2 ) MHP thin-film samples in a half-cell device. There is a comparison of measurements acquiredwith synchrotron radiation and a conventional laboratory source for different times. Changes in composition and core levels binding energies are observed in both cases, indicating a modification of the chemical and electronic properties. The results suggest that changes observed over minutes with highly brilliant synchrotron radiation are likely occurring over hours when working with a lab-based source providing a lower photon flux. The possible degradation pathways are discussed, supported by steady-state photoluminescence analysis. The work stresses the importance of beam effect assessment at the beginning of XPS experiments of MHP samples.