This study investigates the influence of synthesis conditions on structural, morphological and optical properties of chromium-doped hydroxyapatite nanoparticles (Cr-HAp) for UV protection. Using co-precipitation and hydrothermal methods, Cr-HAp nanoparticles with elongated monocrystalline needle-like structures were successfully synthesised. Quantum chemical calculations provided insights into the oriented attachment process and the interaction of ions with the nanoparticle surface. The growth mechanism and dopant distribution were found to be dependent on the nature of the hydroxyl ion source. Optical analysis revealed a distinct absorption peak in the range of 200—350 nm, making these nanoparticles suitable for UVB filter applications. The nanoparticles exhibited a palette of bluish-green hues, with colorimetric properties dependent on synthesis conditions. The Cr-HAp nanoparticles demonstrated great stability as Pickering emulsions, and exhibited enhanced functionality upon vitamin A encapsulation. These findings highlight the potential of Cr-HAp nanoparticles in advanced materials for cosmetics.