Calcium dipicolinate (CaDPA), a major component of bacterial spores, is known to be either a photoprotective or a photosensitizing agent in terms of UV radiation, depending on its hydration state. This molecule is also known to produce numerous photoproducts (DPAp) upon UV exposure, some of which influence spore resistance. The purpose of this study was to better characterize the influence of hydration on the photochemistry of CaDPA using vibrational spectroscopy through three different techniques: Raman, FTIR and O-PTIR microspectroscopy. Synthetic CaDPA was exposed to UVc or UVb in dry conditions or in a water solution. Raman, FTIR and O-PTIR spectra of dry or wet CaDPA were compared before and after irradiation. Results suggest that UVc and UVb exposure mainly affects the bands corresponding to the pyridine ring of CaDPA. However, this effect differs depending on the UV range and the hydration state during UV exposure. Spectra of one DPAp identified in a previous publication as a photosensitizer, named DPAp1, were also acquired by means of the same three spectroscopy techniques. Although DPAp1 comes from a dimerization of two DPA molecules, its spectra appear to be quite different from those of CaDPA. Moreover, this study compares the data provided by O-PTIR, Raman and FTIR spectroscopy via a multiblock analysis. While the information obtained via O-PTIR seems to be closer to that provided by Raman than to that provided by FTIR, the three techniques seem to be quite complementary.