Most cases of lung cancer are caused by smoking, although people who have never smoked can also develop the condition.

Smoking

Smoking cigarettes is the single biggest risk factor for lung cancer. It's responsible for more than 70% of cases. Tobacco smoke contains more than 60 different toxic substances, which 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 cannabis with tobacco. While they tend to smoke less tobacco than people who smoke regular cigarettes, they usually inhale more deeply and hold the smoke in their lungs for longer.

It's been estimated that smoking 4 joints (homemade cigarettes containing a mix of tobacco and cannabis) may be as damaging to the lungs as smoking 20 cigarettes.

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

Passive smoking

If you do not smoke, frequent exposure to other people’s tobacco smoke (passive smoking) can increase your risk of developing lung cancer.

Radon

Radon is a natural radioactive gas that comes from tiny amounts of uranium present in all rocks and soils. It can sometimes be found in buildings.

If radon is breathed in, it can damage your lungs, particularly if you're a smoker. Radon gas causes a small number of lung cancer deaths in England.

Occupational exposure and pollution

Exposure to certain chemicals and substances which are used in several occupations and industries may increase your risk of developing lung cancer. These chemicals and substances include:

• arsenic
• asbestos
• beryllium
• cadmium
• coal and coke fumes
• silica
• nickel

Research also suggests that being exposed to diesel fumes over many years increases your risk of developing lung cancer. One study has shown your risk of developing lung cancer increases by around 33% if you live in an area with high levels of nitrogen oxide gases (mostly produced by cars and other vehicles).