Dual Bioactivity of Curcuminoid Extract from Curcuma longa: Acaricidal Efficacy Against Dust Mites and Anti-Inflammatory Potential in Immune and Skin Cells

House dust mites (HDMs) are major indoor allergens linked to asthma and atopic dermatitis, creating demand for safer, natural alternatives to synthetic acaricides and anti-allergy agents. This study aimed to investigate the dual bioactivity of curcuminoid extract from Curcuma longa to address HDM allergy through two distinct but complementary scopes: an environmental approach evaluating direct acaricidal efficacy to reduce allergen exposure and a cellular approach investigating the anti-inflammatory potential to mitigate the host’s underlying immune response. Curcuminoids were extracted using Soxhlet extraction with 70% ethanol and characterized via TLC, FTIR-ATR, and LC-MS. Acaricidal activity against HDMs was evaluated using extract-impregnated filter papers (0.1–10 mg/mL) over 24 h. Cytotoxicity and anti-inflammatory effects were assessed in HaCaT keratinocytes and RAW264.7 macrophages through cell viability, migration, phagocytic activity, nitric oxide (NO) inhibition, and gene expression assays. The curcuminoid extract demonstrated potent, dose-dependent acaricidal activity against HDM, achieving 100% mortality at 10 mg/mL within 24 h. A safe sub-cytotoxic concentration (≤0.001 µg/µL) preserved HaCaT cell migration and metabolic activity. In LPS-stimulated RAW264.7 cells, curcuminoids significantly reduced inflammatory NO production (p < 0.01) while enhancing phagocytic activity. Overall, these findings highlight curcuminoids as a sustainable natural strategy for reducing HDM exposure and mitigating allergic inflammation.