Causes and risk factors of lung cancer

Lung cancer is the third most common cancer in the UK. Most lung cancers are caused by smoking. There are other factors that can also increase the risk.

What are risk factors?

There are certain things that can increase the risk of developing lung cancer. These are called risk factors. Having a risk factor does not mean you will get cancer. And not having a risk factor does not mean that you will not get it.

If you are worried about lung cancer and would like to talk to someone, we're here. You can:


Smoking tobacco is the cause of most lung cancers and the biggest risk factor. This includes smoking cigarettes, cigars and pipes. The more you smoke, the bigger your risk. Around 9 out of 10 people who get lung cancer (90%) are smokers or ex-smokers. Starting smoking at a young age means the risk is higher.

People who do not smoke can also get lung cancer, but their risk is much lower. About 1 in 10 people who get lung cancer (10%) have never smoked.

When people stop smoking, their risk of lung cancer gets lower over time. After 12 years of stopping smoking, your risk of lung cancer is about 70% lower than people who do smoke. After about 15 years, it is almost the same as a non-smoker.

Passive smoking

Breathing in other people’s cigarette smoke (passive or second-hand smoking) can slightly increase the risk of lung cancer. The risk is much lower than if you smoke yourself.

In the UK, smoking is now banned in most enclosed public places and workplaces.


Lung cancer is more common in older people. More than 4 in 10 people (44%) who are diagnosed are aged 75 and over. Lung cancer can affect younger people, but it is rare under the age of 40.

Radon gas

In certain parts of the UK, a natural gas called radon can pass from the soil into the foundations of buildings. Exposure to high levels of radon is not common. But it can increase the risk of developing lung cancer, particularly in people who smoke as well.


Asbestos was previously used in building industries. People who have been in prolonged or close contact with asbestos have a higher risk of getting lung cancer. The risk is also bigger if they smoke.

Exposure to asbestos also increases the risk of mesothelioma. This is a cancer of the pleura (membranes that cover the lungs). If you worked with asbestos and have lung cancer or mesothelioma, you may be able to claim compensation. Your lung cancer specialist nurse can give you advice on this.

Previous cancer treatment

People have a slightly increased risk of lung cancer if they have previously had radiotherapy to the chest to treat:

The risk is bigger if they smoke.

The benefits of this treatment far outweigh the risk of developing lung cancer.

Lowered immunity


Having a lowered immunity because of illness or treatment can increase the risk of lung cancer. People have a lowered immune system if they:

  • have HIV or AIDS
  • take immunosuppressant drugs after an organ transplant.

Family risk

People with a parent who had lung cancer have an increased risk of developing it. People who have a brother or sister with lung cancer, especially when diagnosed at a younger age, have a higher risk.

Doctors do not know if this could be caused by a lung cancer gene that runs in the family (inherited), or shared risk factors such as smoking.

If you are worried about lung cancer in the family, you may find it helpful to talk to your GP.

Other causes of lung cancer

Rarely, contact with certain chemicals and substances can cause lung cancer – usually through work.

Recent research has shown that air pollution can cause lung cancer. But it is difficult to know the risk for individual people, as it depends on:

  • the air quality where they live
  • how much pollution they are exposed to.

For most people, the risk is very small. Smoking is the major risk factor for lung cancer.

Lung cancer is not infectious and cannot be passed on to other people.