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Passive smoking

Cigarette smoke Breathing in other people's smoke, also called second-hand smoke, can cause cancer. Passive smoking can increase a non-smoker's risk of getting lung cancer by a quarter, and may also increase the risk of cancers of the larynx (voice box) and pharynx (upper throat).

Second-hand smoke can cause other health problems too, including heart disease, stroke and breathing problems. It’s estimated that, every year, second-hand smoke kills over 12,000 people in the UK from lung cancer, heart disease, stroke and the lung disease Chronic Obstructive Pulmonary Disease (COPD).

The chemicals in second-hand smoke

There are two types of tobacco smoke:

  • mainstream smoke, which is directly inhaled through the mouth end of the cigarette, and
  • sidestream smoke, which comes from the burning tip of the cigarette.

Second-hand smoke is made up of sidestream smoke and exhaled mainstream smoke, mixed with the surrounding air.

Sidestream smoke is about four times more toxic than mainstream smoke, although people inhale it in a more diluted form. This is because sidestream smoke contains much higher levels of many of the poisons and cancer-causing chemicals in cigarettes, including:

  • at least three times as much carbon monoxide
  • 10-30 times more nitrosamines
  • between 15–300 times more ammonia.

Second-hand smoke and children

Second-hand smoke is particularly dangerous for children. Children exposed to passive smoke are at higher risk of respiratory infections, asthma, bacterial meningitis and cot death. Second-hand smoke has been linked to around 165,000 new cases of disease among children in the UK each year.

For children, the majority of exposure to second-hand smoke happens in the home. Over twenty percent of children in the UK live in a household where at least one person smokes.

Smoke can spread throughout the home, even if you open the windows. Almost 85 percent of tobacco smoke is invisible and smoke particles might also build up on surfaces and clothes, although the impact of this is not yet clear. If you are a smoker, try to limit your child’s exposure by smoking outside.

Smoking in cars

Second-hand smoke can reach very high levels inside cars because it is a small enclosed space.

During your journey, children in the backseat will be exposed to average smoke levels around three times the European recommended air pollution standard. But the level varies depending on how much you smoke, if you have all the windows fully open or air con on. Peak levels can reach as much as 35 times this recommended level.

Smoking in public places

Since 2007 public spaces, including restaurants, pubs and private members' clubs, have been smoke-free. This helps to protect workers, non-smokers and children from the harmful effects of second-hand smoke. Also since the ban was brought into place, England has seen cigarette smoking rates fall by 10-15%.

Our Policy section has more information on the smokefree legislation and Cancer Research UK’s other tobacco control campaigns such as lobbying for standardised packs.

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Updated: 15 September 2014