Exposure to secondhand smoke is an established cause of coronary heart disease, lung cancer, and premature death.1 Mounting evidence also links such exposure to airway disease, including asthma, chronic obstructive pulmonary disease, and impaired lung function.2 3 4 On the basis of knowledge about these and other serious health effects, North America, Europe, and Australia have introduced smoke-free legislation. None the less, millions of people are still exposed to secondhand smoke in public places in many parts of the world. Globally, passive smoking is responsible for a substantial burden of disease, disability, and mortality. In this context, the linked study by Llewellyn and colleagues (doi:10.1136/bmj.b462) adds cognitive impairment to the list of adverse health effects related to secondhand smoke.5

Although the serious negative health effects of exposure to secondhand smoke are established, we still have much to learn …