Second-hand smoke (SHS) is a complex, dynamic mixture of chemical constituents, all with their own physical and chemical properties. It is difficult to talk about SHS as a single entity, or as if it behaves in a single way. However, the constituents can be divided into 3 basic categories: particulate matter (organic, can be solids or liquids), organic gases (various volatile and semi-volatile organic compounds) and gas-phase inorganic compounds (heavy metals).

Think back to high school chemistry class: anyone remember the Law of Conservation of Mass? Matter is neither created nor destroyed. In any chemical reaction, the mass of the products will be equal to the mass of the reactants. This is just a fancy way of saying that stuff doesn’t disappear into thin air.

Heavier compounds (particulate matter) will fall out of the air and land on surfaces, volatile gaseous chemicals will react in the air with other pollutants and/or sunlight to form new chemical species, other compounds will adsorb (stick to surfaces) or absorb (are taken up by other surfaces) and later desorb (off-gas).

There are more than 4,000 substances given off by the burning end of a cigarette, both in gas and particle phases. The part we can see, and that irritates our eyes, noses and throats, is the particle phase. The part we can’t see, or even necessarily smell, is the gas phase. Regardless of the phase in which they were produced, these chemicals have a nasty habit of hanging around… for a long time. Many individual SHS organic gases are regulated as toxic air contaminants and hazardous air pollutants (U.S. Environmental Protection Agency and the California Air Resources Board).

Second-hand smoke has a dose-response relationship. This means that the more SHS you are exposed to, through your lungs, mucus membranes (eyes, mouth, nose) and skin, the more damage is done to your tissues, which can slowly build up over time. The bigger the dose, the bigger the response.

The science on the health effects of exposure is very solid, and the evidence of harm is irrefutable. Scientific and public health organizations from around the world concur that there is no risk-free level of exposure to SHS and that all exposure should be avoided. This includes:

  • World Health Organization (WHO)
  • International Agency for Research on Cancer (IARC)
  • U.S. Environmental Protection Agency (EPA)
  • California EPA (Air Resources Board identified SHS as a “toxic air contaminant” in June 2005)
  • U.S. Surgeon General
  • British Scientific Committee on Tobacco and Health (SCOTH) and
  • Australian National Health and Medical Research Council.

Health Canada reports over 800 deaths per year are caused by exposure to SHS, but this is a conservative number based on studies of adult exposure in the workplace only. By far the biggest toll is coronary heart disease (25-30% increased risk), followed by lung cancer (20-30% increased risk). Chronic exposure to SHS also causes nasal sinus cancer, breast cancer in predominantly pre-menopausal women (68-120% increased risk), asthma and altered vascular properties (changes to arteries).

In children, exposure to SHS causes pre-term delivery, low birth weight and Sudden Infant Death Syndrome (SIDS). It also causes pneumonia and chronic bronchitis, asthma, middle ear infections, chronic cough, phlegm, wheezing and breathlessness.

There is also suggestive evidence that SHS is linked to stroke, cervical cancer, brain cancer and lymphomas in children, exacerbation of cystic fibrosis, adverse impact on cognition and behaviour, allergic sensitization and miscarriage.

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