Actinic irradiation (i.e. using ionizing light) of EUV pulses on a multilayer Bragg optics was investigated for characterizing the chemical effects. Photothermal effects are ruled out by the low repetition rate and low absolute energy of the EUV pulses. This would exclude the formation of melt-related particles, which have been however observed. Alternative explanations are discussed. The analysis concentrate on the structure and composition of the multilayer stack, with the aim of quantifying the kinetics.