Indoor Nanoparticle Emissions and Exposures during Heat-Based Hair Styling Activities

Heat-based hair styling activities, such as straightening, curling, and waving, emit volatile and semivolatile chemicals when used with hair care products like creams, lotions, and serums. This study investigates the formation of airborne nanoparticles (6-500 nm) during such activities as a previously unrecognized source of indoor air pollution. Experiments conducted in the Purdue zEDGE Test House revealed that hair styling at temperatures above 300 °F produced indoor nanoparticle concentrations ranging from 10,000 to over 100,000 particles cm^-3, with sub-100 nm particles typically accounting for more than 95% of total number concentrations at temperatures exceeding 360 °F. The primary mechanism for nanoparticle formation was heat-driven volatilization of cyclic siloxanes and various low-volatility constituents in hair care products, followed by nanoparticle nucleation and subsequent growth via condensation and coagulation. Ozonolysis of fragrance additives served as a secondary formation pathway. Respiratory tract deposition modeling indicated that more than 10 billion nanoparticles could deposit in the respiratory system during a single hair styling session, with the highest dose occurring in the pulmonary region. These findings identify heat-based hair styling as a significant indoor source of airborne nanoparticles and highlight previously underestimated exposure risks. This work advances our understanding of the physical and chemical processes underlying emissions from personal care product use and underscores the need for mitigation strategies to reduce exposure in residential environments.