Secondhand smoke, also known as environmental tobacco smoke or ETS, is a combination of the smoke coming from the lit end of a cigarette and the smoke exhaled by a person smoking.

Public health officials have concluded that secondhand smoke from cigarettes causes disease, including lung cancer and heart disease, in non-smoking adults, as well as causes conditions in children such as asthma, respiratory infections, cough, wheeze, otitis media (middle ear infection) and Sudden Infant Death Syndrome. In addition, public health officials have concluded that secondhand smoke can exacerbate adult asthma and cause eye, throat and nasal irritation.

The public should be guided by the conclusions of public health officials regarding the health effects of secondhand smoke when deciding whether to be in places where secondhand smoke is present, or if they are smokers, when and where to smoke around others. Particular care should be exercised where children are concerned and adults should avoid smoking cigarettes around them.

The conclusions of public health officials concerning environmental tobacco smoke are sufficient to warrant measures that regulate cigarette smoking in public places. In places where cigarette smoking is permitted, the government should require the posting of warning notices that communicate public health officials' conclusions that secondhand smoke causes disease in non-smokers.