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Middlesex-London Health Unit

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Second-Hand Smoke

There is no safe level of second-hand smoke; it can be harmful even when you can't see it or smell it.

What is second-hand smoke?

Second-hand smoke is a mix of two kinds of smoke:1,6,7

  1. Smoke exhaled from a smoker.
  2. Smoke from the end of a lit tobacco product, such as a cigarette, waterpipe, or cigar.

Facts about Second-Hand Smoke

  • It is toxic and contains over 7,000 chemicals; 69 of these chemicals can cause cancer.1,2,6,7
  • It contains the same harmful chemicals as the smoke inhaled directly from the cigarette, but some chemicals could be in higher amounts.1,3,4,6
  • Harmful chemicals from second-hand smoke remain in materials and fixtures long after someone has smoked there (this is called third-hand smoke).3,6,8
  • Exposure to second-hand smoke, even if you have never smoked before, increases your risk of lung cancer, lung disease, heart disease and stroke.1,6,7
  • Babies and young children are especially vulnerable to the effects of second-hand smoke.1,3,7
  • Only some of the smoke from a cigarette is actually inhaled by the smoker. The majority of the smoke enters the air around the smoker.4
  • Smoke can travel in a number of ways between rooms in a home or units in a building, such as through vents, doorways, and fixtures, like outlets, plumbing, and ceiling fans.1,4,7,8
  • Second-hand smoke is not removed by the following; air purifiers and filters, opening windows, turning on a fan, closing doors or using air fresheners. Some of these may remove the odour, but not the harmful effects.1,4,6,8
  • Second-hand smoke is harmful even outdoors.4,7
  • There are laws banning smoking in workplaces and public places to protect against second-hand smoke exposure.5

Minimizing your Risk

  • Make your home smoke-free, meaning no smoking is allowed in any room of the house. If you or your partner smokes, take it outside.1,4
  • Make your car smoke-free. Smoking in vehicles with passengers less than 16 years of age is illegal in Ontario, regardless of whether or not the car is moving, or whether or not any windows or doors are open.5
  • Keep your children smoke-free; refrain from smoking around them even in outdoors spaces.4,7
  • Remove ashtrays, lighters, matches, pipes etc. from your home and car.4
  • Place smoke-free signs on entrances to your home.4
  • Choose childcare providers who don't smoke in their homes or near your children.1,4
  • If you must use tobacco, wash your hands, change your clothes and brush your teeth before interacting with others.4

For more information, please contact the Middlesex-London Health Unit Tobacco Control Team.

Date of creation: October 31, 2012
Last modified on: September 25, 2017


11American Cancer Society. (2015). Health Risks of Second-hand Smoke. Retrieved from
2American Lung Association. (2017). What’s in a Cigarette? Retrieved from
4Government of Canada. (2015). Make Your Home and Car Smoke-free. Retrieved from
5Government of Ontario. (2016). Smoke-Free Ontario. Retrieved from
6National Cancer Institute. (2011) Secondhand smoke and cancer. Retrieved from
7Smoke-Free Ontario Scientific Advisory Committee, Ontario Agency for Health Protection and Promotion (Public Health Ontario). Evidence to guide action: Comprehensive tobacco control in Ontario (2016). Toronto, ON: Queen's Printer for Ontario. Retrieved from
8Non-Smokers’ Rights Association (NSRA) and Smoking and Health Action Foundation (SHAF). (March 2013) When Neighbours Smoke: A Tenants Guide. Toronto, ON: Non-Smokers’ Rights Association. Retrieved from
9Smoking and Health Action Foundation. (2014) Thirdhand Smoke: An Emerging Issue (fact sheet). Retrieved from