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 younger age increases the risk. In the UK, 72% of lung cancer cases are caused by smoking.

When people stop smoking, their risk of lung cancer gets lower over time. After 12 years of not smoking, the risk of getting lung cancer is about 70% lower than it is for people who still smoke. After about 15 years, it is almost the same as a non-smoker.

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.

We have more information about giving up smoking.

Related pages

Passive smoking

Breathing in other people’s cigarette smoke is called passive or second-hand smoking. It 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 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 in anyone under 40.


Asbestos is a material that was previously used in the building industry. People who have been in prolonged or close contact with asbestos have a higher risk of getting lung cancer. The risk is greater if they smoke.

Exposure to asbestos also increases the risk of cancer of the pleura. This is called mesothelioma. The pleura are the 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.

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 also smoke.

Air pollution

Recent research has shown that air pollution can increase the risk of lung cancer. The risk is linked to air quality and how much pollution a person is exposed to. For most people, the risk is very small. Smoking is the major risk factor for lung cancer.

Chemicals and other substances at work

Rarely, contact with certain chemicals and substances can increase the risk of lung cancer. Contact with these substances is usually through work. For example, you have an increased risk if you work with:

  • asbestos
  • silica
  • arsenic
  • radiation.

Being exposed to diesel fumes through work can also increase lung cancer risk. For most people, the risk is very small.

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 higher if they smoke. The benefits of this treatment far outweigh the risk of developing lung cancer, especially as these cancers can be cured.

Lowered immunity

Having 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 have a higher risk, especially if they were diagnosed at a younger age.

Doctors do not know why this is. It could be caused by a lung cancer gene that runs in the family (inherited). Or it could be caused by shared risk factors such as smoking.

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

About our information

  • References

    Below is a sample of the sources used in our lung cancer information. If you would like more information about the sources we use, please contact us at

    National Institute for Health and Care Excellence (NICE). Lung cancer – Diagnosis and management. Clinical guideline 2019.

    Metastatic non-small cell lung cancer: ESMO clinical practice guidelines for diagnosis, treatment and follow-up. 2018.

    European Society for Medical Oncology (ESMO). Early and locally advanced non-small-cell lung cancer (NSCLC): ESMO clinical practice guidelines for diagnosis, treatment and follow-up. 2017.

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr David Gilligan, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 November 2020
Next review: 01 November 2023

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.