What causes lung cancer?

Smoking is the leading preventable cause, but lung cancer can also occur in people who have never smoked. Second-hand smoke, radon, workplace substances such as asbestos, air pollution, and previous radiation to the chest may contribute to risk.

Damage can build up in the instructions that control a lung cell's growth and repair. A changed cell may then multiply when it should stop, forming a tumour that can invade nearby tissue or spread elsewhere. Different lung cancers carry different molecular changes, and the exact trigger in one person is not always identifiable.

A risk factor increases the possibility of disease but does not prove why an individual developed it. Having a risk factor does not mean cancer is inevitable, and lacking a recognised exposure does not rule it out.

If you smoke, stopping reduces further exposure at any age; a clinician or stop-smoking service can help with medicines and behavioural support. Keep homes and cars smoke-free. If radon is a concern, ask the relevant local authority or a qualified testing service about assessment.

Follow protective procedures around dust, fumes, asbestos, diesel exhaust, silica, or other workplace hazards. Tell your clinician about smoking history, second-hand smoke, occupational exposure, and any earlier chest radiotherapy so they can decide whether assessment is appropriate.

Arrange a medical appointment for a cough that persists or changes, coughing up blood, unexplained breathlessness, recurring chest infections, chest or shoulder pain, unexplained weight loss, or a hoarse voice that does not settle. These symptoms have many possible causes, but they warrant assessment.

Seek urgent care for severe difficulty breathing, a large amount of coughed-up blood, fainting, confusion, or intense chest pain. Urgency is based on the severity of the symptom, not on whether cancer is thought to be common.

Ask which parts of your exposure and health history matter, whether your symptoms need imaging or other tests, and what support is available to stop smoking. If lung cancer is diagnosed, ask whether testing the tumour for molecular changes could help guide treatment choices.