Impact of scented candle use on indoor air quality and airborne microbiome.

Indoor air quality has become a growing concern worldwide due to its significant impact on human health, particularly in residential environments where people spend most of their time. Many studies have examined particulate matter (PM) in indoor air and indoor bioaerosols. However, there is a significant lack of research on airborne micro-sized bacteria (m-AB) and nano-sized bacterial extracellular vesicles (n-ABE), particularly those produced by common household activities, such as burning scented candles. This study investigates changes in PM concentrations and indoor microbiome composition resulting from candle use. Air samples were collected from three locations in residential homes: at the candle-lit spot (CL), 3 m away (3m_CL), and 6 m away (6m_CL). PM concentrations peaked at 1.52 times the baseline at the source after 5 min of burning, while PM and PM remained elevated at 3m_CL and 6m_CL over time. Before burning, dominant m-AB genera included Phyllobacterium and Pseudomonas, while post-burning, Phyllobacterium myrsinacearum in n-ABE significantly increased, marking its first detection in indoor air. This suggests that existing airborne bacteria may undergo growth or apoptosis due to combustion byproducts. These findings highlight the importance of improving ventilation in indoor spaces to minimize health risks from prolonged exposure to airborne particles and bacterial vesicles.