Mechanically driven aerosol emissions from electric toothbrushing: An overlooked indoor source with exposure and...

Indoor aerosol emissions are predominantly attributed to respiratory activities, whereas non-respiratory sources associated with routine hygiene behaviors remain largely overlooked. Here, we investigated aerosol generation during electric toothbrushing through 1290 controlled chamber tests involving human participants. Results showed that emissions were dominated by respirable fine particles, with over 85% below 2.5 μm, while ultrafine particle levels showed no clear increase relative to the pre-brushing baseline, indicating a distinct emission regime compared to respiratory processes. Emission dynamics exhibited structured temporal patterns with sustained release, rather than short-lived bursts. Across device-, product-, and subject-level factors, aerosol generation was primarily governed by toothbrush mechanics, with sonic toothbrushes producing consistently higher emissions than oscillating-rotating types, highlighting the role of bristle vibration frequency and amplitude, whereas toothpaste formulation showed secondary, mechanism-dependent effects, and inter-individual variability remained negligible. These findings suggest that mechanically induced liquid-film disruption dominates aerosol formation. Measured emission rates were comparable to those from speaking and approached the lower range of singing. Dose-response modeling further indicated that, under assumed pathogen concentrations and aerosol viability conditions, high-emission sonic brushing could produce modeled relative infection-risk estimates comparable to speaking, while Monte Carlo rank analysis placed it among the higher-ranked activity scenarios below singing. Notably, subjective perception did not reflect measured emissions, indicating an unrecognized exposure pathway. Overall, electric toothbrushing is identified as a previously overlooked, mechanically driven indoor aerosol source with non-negligible implications for exposure and infection risk, highlighting the need to incorporate hygiene-related emissions into indoor air quality and infection risk assessments.