Is secondhand smoke associated with mental health issues? A narrative review of the evidence and policy implications.

Secondhand smoke (SHS) is a well-established cause of lung cancer, respiratory disease, heart disease and developmental issues in children, with an overwhelming evidence base spanning over four decades. In this narrative review, we describe studies which have also linked self-reported or cotinine-assessed SHS exposure in the home, workplace and other settings to mental health disorders including depression, suicide, anxiety, and psychological distress in children and adults, sleeping disorders, Attention Deficit Hyperactivity Disorder and behavioural issues in children, and dementia in older adults. In general, evidence indicates that SHS exposure is associated with these disorders in a dose-response manner, with higher odds reported in people who are exposed to SHS at high levels, frequently, and in the home environment. Most studies so far are cross-sectional albeit in large, nationally representative samples from various countries with a smaller number of longitudinal studies. More research is needed in this area to determine whether SHS is a direct cause of adverse mental health outcomes, and whether creating smokefree environments leads to improved mental wellbeing. In particular, more research is needed on the impact of smokefree home environments, an area which has received relatively little focus in smokefree interventions which generally target public places.