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What causes lung cancer?

A risk factor is any factor that is associated with an increased chance of developing a particular health condition, such as lung cancer. There are different types of risk factors, some of which can be modified and some which cannot.

It should be noted that having one or more risk factors does not mean a person will develop lung cancer. Many people have at least one risk factor but will never develop lung cancer, while others with lung cancer may have had no known risk factors. Even if a person with lung cancer has a risk factor, it is usually hard to know how much that risk factor contributed to the development of their disease.

While the causes of lung cancer are not fully understood, there are a number of factors associated with the risk of developing the disease. These factors include:

  • tobacco smoking
  • environmental factors such as passive smoking, random exposure and occupational exposures, such as asbestos and diesel exhaust
  • a family history of lung cancer
  • previous lung diseases such as lung fibrosis, chronic bronchitis, emphysema and pulmonary tuberculosis.

Smoking

Smoking cigarettes is the single biggest risk factor for lung cancer. 

Tobacco smoke contains more than 60 different toxic substances, which can lead to the development of cancer. These substances are known to be carcinogenic (cancer-producing).

If you smoke more than 25 cigarettes a day, you are 25 times more likely to get lung cancer than a non-smoker.

While smoking cigarettes is the biggest risk factor, using other types of tobacco products can also increase your risk of developing lung cancer and other types of cancer, such as oesophageal cancer and mouth cancer. These products include:

  • cigars 
  • pipe tobacco 
  • snuff (a powdered form of tobacco) 
  • chewing tobacco.

Smoking cannabis has also been linked to an increased risk of lung cancer. Most cannabis smokers mix their cannabis with tobacco. While they tend to smoke less than tobacco smokers, they usually inhale more deeply and hold the smoke in their lungs for longer.

Even smoking cannabis without mixing it with tobacco is potentially dangerous. This is because cannabis also contains substances that can cause cancer.

Passive smoking

Even if you do not smoke, frequent exposure to other people's tobacco smoke (passive smoking) can increase your risk of developing lung cancer. For example, research has found that non-smoking women who share their house with a smoking partner are 25% more likely to develop lung cancer than non-smoking women who live with a non-smoking partner.

 Sources: Cancer Australia (What is lung cancer), NHS Choices, UK (Causes of lung cancer)

Last reviewed: August 2015

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