A comprehensive analysis is carried out to investigate the high-frequency (HF) oscillations and their leading causes in dc microgrids. The analysis relies on the impedance-based stability criterion. It is shown for the first time that all types of DGs and loads contribute to the HF oscillations in a dc microgrid. This is in contrast with the previous studies that designate constant-power loads as the main cause for the interaction dynamics in dc microgrids. It is noted that different factors including number of DGs, load dynamics, load powers, and the type of resonances affecting the HF voltage/current oscillations are taken into account in our studies. A closed-form expression is derived for the estimation of the damping factor of dominant HF modes of dcmicrogrids. Moreover, a proper damping approach is proposed to reduce the HF oscillations. Various simulation studies are presented to evaluate the effectiveness of the proposed analysis approach.