Introduction A major site of secondhand smoke exposure for children and adults is the home. Few studies have evaluated the impact of e-cigarette or hookah use on home air quality, despite evidence finding toxic chemicals in secondhand e-cigarette aerosols and hookah smoke. We assessed the effect of e-cigarette and hookah use on home air quality and compared it with air quality in homes where cigarettes were smoked and where no smoking or e-cigarette use occurred.

Methods Non-smoking homes and homes where e-cigarettes, hookah or cigarettes were used were recruited in the New York City area (n=57) from 2015 to 2019. Particulate matter with diameter less than 2.5 µm (PM_2.5), black carbon and carbon monoxide (CO) were measured during a smoking or vaping session, both in a ‘primary’ smoking room and in an adjacent ‘secondary’ room where no smoking or vaping occurred. Log transformed data were compared with postanalysis of variance Tukey simultaneous tests.

Results Use of hookah significantly increased PM_2.5 levels compared with non-smoking homes, in both the primary and secondary rooms, while use of e-cigarettes increased PM_2.5 levels only in primary rooms. Additionally, in-home use of hookah resulted in greater CO concentrations than the use of cigarettes in primary rooms.

Conclusions Use of e-cigarettes or hookah increases air pollution in homes. For hookah, increases in PM_2.5 penetrated even into rooms adjacent to where smoking occurs. Extending smoke-free rules inside homes to include e-cigarette and hookah products is needed to protect household members and visitors from passive exposure to harmful aerosols and gases.