The widespread use of hazardous ingredients, such as hydroquinone (HQ) and methylparaben (MP), in cosmetic products poses significant public health and safety risks, underscoring the urgent need for rapid and reliable analytical tools. To address this critical gap, we report the development of a highly efficient electrochemical sensor for the simultaneous detection of HQ and MP. The sensor is based on a glassy carbon electrode (GCE) that is synergistically modified with a novel Pt nanocubes/TiO2/multi-walled carbon nanotubes (PtNCs/TiO2/MWCNTs) nanocomposite. The optimal composition of the nanocomposite was rigorously determined using a simplex lattice mixture design, which maximised the electrochemical oxidation current. The resulting optimized nanocomposite was then synthesized, structurally characterized using SEM-EDS and TEM, and subsequently drop-cast onto the glassy carbon electrode (GCE) surface. The sensor's performance was systematically investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), exhibiting well-defined oxidation peaks with wide linear detection ranges (4–350 μM for HQ and 10–5000 μM for MP), and remarkably low limits of detection (0.201 μM for HQ and 0.50 μM for MP). Furthermore, the sensor demonstrated exceptional repeatability and stability (RSD < 5%), high selectivity against common interferents, and excellent accuracy (recovery values ranging from 98.4% to 102.5%) when applied to commercial facial whitening creams. In conclusion, the developed PtNCs/TiO₂/MWCNTs-modified GCE provides a practical, sensitive, and cost-effective platform for accurate, continuous monitoring of cosmetic safety. © 2026 Elsevier B.V.