The exposure to inhalable substances and their impact on the safety assessment of cosmetic products and their ingredients

Background and Objectives. Inhalation exposure to cosmetic ingredients can pose health risks, especially in sprays and powders where airborne particles reach the lower respiratory tract. Assessing the safety of titanium dioxide (TiO₂), quartz, and Aerosil (amorphous silica) is crucial to ensure their safe cosmetic use. This study aimed to evaluate the effects of these substances on cellular viability and epithelial barrier integrity using a human threedimensional (3D) bronchio alveolar tissue model (EpiAirway) at a relevant concentration of 120 ppm. Materials and Methods The EpiAirway model (MatTek, AIR100) consists of highly differentiated human tracheobronchial epithelial cells forming multiple layers with tight junctions and beating cilia, realistically reproducing the respiratory epithelium. Tissues were treated every 48 hours with TiO₂, quartz, or Aerosil diluted in EpiAirway MUCUS (1:10 in TEER buffer). Barrier integrity was monitored through transepithelial electrical resistance (TEER) measurements on days 2, 5, and 7, while cell viability was evaluated by the MTT assay at day 7. Data were normalized to the negative control and analyzed in triplicate. Results TEER measurements showed no significant differences between treated tissues and controls at any time point, indicating preservation of epithelial barrier function. The MTT assay revealed that TiO₂ and Aerosil did not reduce cell viability, while quartz caused an average 27% decrease compared with the control, suggesting a potential cytotoxic effect. Discussion and Conclusion The results confirm the suitability of 3D tissue models as advanced tools for inhalation safety assessment of cosmetic ingredients, offering more predictive data than traditional 2D systems and aligning with the ethical principles of the 3Rs. Exposure to TiO₂ and Aerosil did not compromise tissue viability or integrity, whereas quartz induced moderate cytotoxicity that warrants further investigation into possible inflammatory, oxidative, and transcriptomic responses.