Pan et al. (Am J Epidemiol. 2018;187(5):911-918) reported findings that exposure to secondhand smoke (SHS) was associated with cognitive decline over the course of 2 years among middle-aged and older Chinese women who never smoked, and they also reported a dose-response relationship. SHS exposure affects vulnerable people disproportionately because they have less control or choice over their living and working environment. Smoking is an established risk factor for dementia, but recent evidence reports on dementia-risk increase have not included SHS. Many epidemiologic studies collect data on smoking but not SHS exposure. SHS may be one of the most prevalent and modifiable risk factors for cognitive decline and therefore represents a major potential target for reduction of dementia risk. Given the high prevalence of smoking in China and other parts of the world, there is an urgent need to raise awareness of SHS reduction as part of global and national strategies to reduce cognitive decline and dementia and to introduce legislation that protects nonsmokers and vulnerable children and adults from SHS.