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Health effects of secondhand smoke

It's well known that smoking is bad for your health but the risks of breathing in someone else's cigarette smoke also poses significant health risks. Exposure to this kind of smoke is known as secondhand smoking (SHS) or passive smoking. It can also be referred to as 'environmental tobacco smoke'.

What is secondhand smoke?

When someone smokes, most of the smoke is not drawn into the smoker's lungs. Instead, most of it is released into the air where it can be inhaled by non-smokers. Tobacco smoke contains some 4,000 chemicals and more than 50 of these have been associated with cancer. The chemicals can stay in the air for up to two and a half hours, even in a well ventilated room. The risks are also high if you are inside an enclosed space, such as a vehicle.

What types of chemical are released?

  • Hydrogen cyanide -- a highly poisonous gas used in chemical weapons and pest control
  • Benzene - found in petrol
  • Formaldehyde -- a preservative used to embalm dead bodies
  • Carbon monoxide -- a poisonous gas found in car exhaust

Which kind of smoke is harmful?

All forms of tobacco smoke are harmful including:

  • Cigarettes
  • Pipe tobacco
  • Cigars
  • Hand rolled cigarettes

The risks of secondhand smoke

The UK Charity Action on Smoking and Health (ASH) says more than 50 studies of passive smoking have been carried out over the past 25 years. Most show an increased risk, especially among people who have a high level of exposure. The effects of secondhand smoke can occur straight away. Symptoms may include:

ASH says there is no safe level of exposure to tobacco smoke and there are long-term health effects, especially with continued exposure over time. These include:

Heart disease

Research has shown that frequent exposure to secondhand or passive smoke can increase your risk of cardiovascular disease, which in turn, can increase risk of heart attacks, heart failure or stroke.

Studies show that it takes as little as 10 minutes for the smoke to start causing damage. Smoke exposure:

  • Makes your blood platelets stickier
  • Raises your LDL, or "bad" cholesterol, levels
  • Damages the lining of your blood vessels

These effects make you more susceptible to a blockage that leads to a heart attack or stroke. Researchers have found that women who have been exposed to secondhand smoke face a 69% higher risk of heart disease and a 56% higher risk of stroke than those who haven't been exposed.


Various studies have shown that passive smoking can cause damage to the lungs of non-smokers. While lung cancer is the most well known risk of secondhand smoke exposure, the risks of breast cancer, cervical cancer and other types of cancer are also believed to be higher

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