Indoor Smoking Bans and Children’s Health Outcomes in Japan

Passive smoking has long been recognized as a public health threat that imposes negative externalities on non- smokers. To address this issue, Japan implemented a nationwide indoor smoking ban in April 2020, prohibiting smoking in public spaces. We hypothesize that the ban has a more direct impact on families with at least one smoker, as they are more likely to visit public areas where smoking was allowed. Consequently, the policy reduces opportunities for public smoking among these individuals, thereby lowering their children's exposure to second-hand smoke. We examine whether this policy improved the health outcomes of children from smoking households by analyzing the probability of asthma diagnoses among children under two years old in Japan. Using JMDC Claims Database monthly data from 2018 to 2023, we find that children in smoking households have a higher probability of being diagnosed with asthma compared to those in non-smoking households. This gap gradually narrowed after the implementation of the smoking ban. An event study analysis that accounts for staggered policy exposure based on children's birth time shows that the probability of asthma diagnosis among children in smoking households decreased significantly one year after the intervention. An intensity-of-treatment analysis that examines the policy’s effect based on time elapsed since the intervention also reveals a significant reduction in asthma diagnoses among the treated group in 1 to 1.5 years following the smoking ban. These results are robust to environmental factors, such as the COVID-19 pandemic, under the assumption that treated and control groups were similarly affected by the pandemic.