Second-hand smoke (SHS) is a mixture of tobacco smoke and ambient air. SHS may be produced by cigarettes or other smoking devices, and is a combination of mainstream smoke (exhaled by the smoker) and sidestream smoke (emitted by the burning end of the tobacco product).[2,3] Approximately two thirds of the smoke from a burning cigarette enters the surrounding environment and may be inhaled by people in the area. SHS may also be referred to as environmental tobacco smoke, involuntary smoking, or passive smoking.
SHS comprises more than 4,000 chemicals emitted from burning tobacco, of which at least 250 are known to be carcinogenic or toxic. Some chemicals found in SHS include arsenic, benzene, beryllium, cadmium, chromium, ethylene oxide, nickel, and vinyl chloride. Compared to the smoke that is inhaled by smokers, SHS has over two times the amount of nicotine and tar, and five times the amount of carbon monoxide.
The primary route of exposure to SHS is inhalation.[2,3] The complexity of SHS mixtures leads to difficulties in assessing exposure. As surrogate measures of SHS exposure, research and public health studies typically monitor levels of nicotine, carbon monoxide, benzene, and respirable particulates suspended in air, or biomarkers such as levels of nicotine metabolites in saliva, blood or urine.[3,6]
SHS is classified by the International Agency for Research on Cancer (IARC) as Group 1, carcinogenic to humans, with a well-established link to lung cancer.[2,3] An IARC review of Group 1 agents in 2012 reaffirmed this classification and included larynx and pharynx as "tumour sites for which there is limited evidence." 
Other adverse health effects associated with exposure to SHS include eye, nose and throat irritation, dizziness, and nausea. Children exposed to SHS may experience chronic respiratory illness, impaired lung function, and middle ear infection. SHS can aggravate allergies or asthma symptoms, and long-term exposure has been linked to heart disease.[2,4] Health Canada estimates that over 1,000 non-smokers die in Canada each year as a result of SHS exposure.
In Canada, regulations governing environmental or occupational protection from SHS are administered by federal, provincial, and municipal governments. Federal regulations apply to federal lands and corporations, as well as federally regulated areas (i.e., transportation, communications, and banking). Provincial regulations can ban or restrict smoking in workplaces or public places, whereas municipalities have the authority to introduce additional restrictions within their geographic boundaries.
Non-Smokers' Health Act
Regulates smoking in federal workplaces and on common carriers; amends Hazardous Products Act's cigarette advertising regulations
Tobacco and Smoking Reduction Act
Tobacco and Vapour Products Control Act Motor Vehicle Amendment Act Bill 14: Tobacco Control Amendment Act
2007 2008 2015
The Non-Smokers' Health Protection Act The Highway Traffic Act The Non-Smokers Health Protection Amendment Act (E-Cigarettes)
2013 2009 2015
Smoke-free Places Act
Smoke-free Environment Act
Smoke-free Places Act
Tobacco Control Act Occupational Health and Safety Regulations, Section 81 Environmental Tobacco Smoke Work Site Regulations (Under the Safety Act)
2010 2015 2004
Tobacco Control Act Tobacco Control Regulations Environmental Tobacco Smoke Work Site Regulations (Under the Safety Act)
2013 2007 2003
Smoke-free Ontario Act
Smoke-free Places Act
The Tobacco Control Act The Occupational Health and Safety Regulations (Under the Occupational Health and Safety Act)
Smoke-Free Places Act
Legislation to ban smoking is mostly consistent across provincial and territorial jurisdictions. Smoking is prohibited in nearly all enclosed public places and places of employment in all provinces. However, not all First Nations territories have applied such bans to their communities. The majority of provincial legislation no longer permits smoking in separate designated smoking rooms or areas (DSRs/DSAs), although group living, long-term care facilities, and designated smoking hotel rooms are common exceptions. Amendments to provincial smoking legislation ban smoking in vehicles when children are present. Depending on the province, the maximum age for "children" ranges between 16 and 19, inclusive. Legislation does not cover smoking in private homes. Some provinces prescribe additional areas where smoking is prohibited, including school grounds and outdoor patios. Other provinces continue to permit smoking on outdoor patios, with restrictions relating to the percentage of the patio that is enclosed. Most recent amendments have incorporated restrictions on use of e-cigarettes and other smoking devices in public places and workplaces. 
Many municipalities have passed more restrictive bylaws to provide additional protection from SHS. Examples of municipal bylaws include smoking bans on outdoor patios and in public outdoor areas such as playgrounds and parks, hotel rooms, and private vehicles. Bylaws may also include buffer zones around entranceways, air intakes, and windows.[38,39]
The most important route of occupational exposure to SHS is inhalation.
CAREX Canada estimates that approximately 418,000 Canadian workers, or 2% of all Canadian workers, are exposed to SHS at work. The group of workers with the largest number of exposed individuals is trades, transport, and equipment operators. This group also has the highest rates of exposure, with an estimated 9% of workers being exposed. Other occupation groups with SHS exposure are sales and service, primary industry, and management.
Non-occupational exposures to SHS can occur in a variety of indoor and outdoor, private and public settings.
Survey results from CTUMS for exposure to SHS show little difference between 2009 and 2012; approximately 34% of respondents in both years indicated that they were exposed to second-hand smoke at least once a week.[40,41] However, daily exposure to second-hand smoke declined from 18% in 2012 to 21% in 2009.[40,41]
The most common reported sites of exposure in 2009 were building entrances (54%), followed by sidewalks or parks (53%), inside vehicles (20%), and at the workplace (20%). In 2012, the most common reported sites of exposure were sidewalks or parks (54%), followed by building entrances (51%), at the workplace (21%), and inside vehicles (18%).
Our team has performed a detailed scan of exposure control resources and assembled a compilation of key publications and resources. These are organized by type of exposure (environmental or occupational) and by specificity (general or carcinogen-specific). Please visit our Exposures Reduction Resources page to view.
We also recommend exploring the Prevention Policies Directory, a freely-accessible online tool offering information on policies related to cancer and chronic disease prevention. Providing summaries of the policies and direct access to the policy documents, the Directory allows users to search by carcinogen, risk factor, jurisdiction, geographical location, and document type. Click here to learn more about policies specific to SHS in the Directory. For questions about this resource, please contact a member of the Prevention Team at the Canadian Partnership Against Cancer at email@example.com.