It’s been four years since Japan banned indoor smoking at large restaurants, offices and many other public places. As the world marks World No-Tobacco Day on Friday, debate is growing over passive smoking in one crucial space that remains unregulated: private homes.

The revised Health Promotion Act that took effect in April 2020 does not cover passive smoking in living spaces — a concern in Japan, where many people live in multiunit apartment buildings or small houses crammed together with little space between them.

Exposure to secondhand smoke that wafts over from a neighbor's balcony could cause serious health issues. It has been long established that secondhand smoke raises the risk of lung cancer and other diseases among nonsmokers.