In this study, we investigate the influence of an admixed fermionic dark matter (DM) component on the equilibrium structure of white dwarfs (WDs). We adopt a single-fluid description in which dark matter couples to baryonic matter through the Higgs portal, and the baryonic and DM contributions to the total energy density and pressure are treated within a unified framework in the locally equilibrated regime. We examine how variations in DM particle mass ($m_{\chi }$) and DM fraction ($f_{\chi }$) modify the equation of state (EoS), the mass-radius relationship, and the internal mass and pressure distributions of WDs. Our results show that the presence of DM softens the EoS, with lighter DM particles providing stronger pressure support and leading to more extended stellar structures. Increasing the DM fraction leads to a more compact configuration, reducing both the WD’s radius and maximum mass. We further demonstrate that heavier DM particles enhance stellar compactness and can eventually drive the star toward gravitational instability. Moreover, the analysis of the mass-radius relationship reveals that while small fractions of DM are consistent with observed WD masses, the radii predicted by our models are smaller than observations, suggesting additional influences such as rotation or magnetic fields. Global dynamical stability is analyzed by computing the squared frequency ${\omega }^2$ of the fundamental radial mode within the single-fluid framework. We find that ${\omega }^2>0$ throughout the stable branch of solutions in the explored parameter range, indicating that moderate DM admixtures do not induce dynamical instability. Overall, our results demonstrate that the single-fluid formalism, previously applied to other compact stars, can be consistently extended to white dwarfs and provides a controlled framework for studying the structural impact of dark matter admixtures.

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• Dark matter
• General relativity
• Particle astrophysics
• Particle dark matter