Size-Segregated Incense Aerosols Drive ROS–Mitochondrial Dysfunction and Programmed Cell Death Across Human Cell Types

Incense burning is a major indoor source of fine and ultrafine particulate matter (PM), yet the size-chemistry determinants of its cellular toxicity remain underdefined. We characterized aerosols from three commonly used incense types using Aerodynamics Particle Sizer (APS)/Scanning Mobility Particle Sizer (SMPS) for sizing, Micro-Orifice Uniform Deposit Impactor (MOUDI) for size segregation, and water-soluble phase (WP) or organic-phase (OP) extraction to generate incense aerosol extracts (IAEs). Across A549, HEK293T, and SH-SY5Y cells, OP-IAEs from fraction III (0.18-0.10 μm) and IV (<0.10 μm) exhibited the strongest cytotoxicity, oxidative responses, and mitochondrial dysfunction. Type A incense (sandalwood-dominant) IAEs consistently showed the highest potency among the investigated incenses. Mechanistic assays revealed that ultrafine OP-IAEs, elevated intracellular H₂O₂, decreased mitochondrial membrane potential (MMP), depleted ATP, and activated apoptosis (caspase-3), pyroptosis (caspase-1), and autophagy-associated pathways. Moreover, ≥80% of all emitted particles were <0.18 μm and were disproportionately enriched in OP constituents across incense types. Collectively, these results identify ultrafine, lipophilic aerosol fractions as key drivers of oxidative-mitochondrial injury and programmed cell death, establishing a size- and phase-resolved framework for assessing incense-related health risks and for guiding exposure mitigation in incense-rich indoor environments.