Smoking is the main cause of lung cancer and about 90% of cases are due to this (17,18).
The risk of lung cancer increases with the number of cigarettes smoked, number of smoking years, early smoking age, amount of tar and nicotine content, and use of rolling tobacco and non-filtered cigarettes (19, 20)
Passive smoking is also a risk factor. The risk for developing lung cancer increases by 20–30 % when living with a smoker compared to living with a non-smoker (21).
Other risk factors may be air pollution, radon gas, asbestos, and nickel and chromium exposure (22).