What Causes Lung Cancer — Risk Factors Explained

Tobacco smoking is by far the main cause of lung cancer worldwide. The smoke contains thousands of chemicals, dozens of which are known to cause cancer, and these damage the DNA inside the cells lining the airways over many years. Risk depends on both how much and how long a person has smoked, and it applies to cigarettes, bidis, hookah and cigars. That said, smoking is not the only cause: radon gas, second-hand smoke, air pollution, asbestos and family history all contribute, and a meaningful number of cases occur in people who have never smoked. Understanding all of your risks, not just smoking, is the most useful starting point.

Yes. While smoking is the largest single risk factor, lung cancer also affects people who have never smoked, and these cases are often missed because no one expects them. In non-smokers, the common causes include second-hand smoke, radon gas building up indoors, long-term air pollution, and workplace exposures such as asbestos, diesel exhaust and certain chemicals. A family history of lung cancer also raises risk. In some non-smokers, the cancer is driven by specific genetic changes in the tumour, which molecular testing can identify and which may open up targeted treatments. The key message is that a persistent cough, breathlessness or other warning sign deserves a check in anyone, smoker or not.

Tobacco smoke contains many cancer-causing chemicals. Each time smoke is inhaled, these substances reach the delicate lining of the airways and damage the DNA inside lung cells. The body repairs much of this damage, but not all of it. Over years, faults accumulate in the genes that control how cells grow and divide, and when enough build up, a cell can begin to grow uncontrollably and form a cancer. This gradual process is why risk rises with how much and how long someone has smoked, and why lung cancer becomes more common with age. The encouraging part is that stopping smoking lowers risk over time, with benefit beginning within a few years of quitting.

Yes. Radon is a natural radioactive gas that comes from the breakdown of uranium in soil and rock. It is invisible and odourless, and it can seep into buildings and collect indoors, especially in poorly ventilated lower floors. When breathed in over a long time, the radiation it gives off can damage lung tissue and lead to cancer. Health agencies recognise radon as a leading cause of lung cancer in non-smokers and a significant cause overall, second only to smoking in some regions. The risk is much higher for people who also smoke. Where radon is a known concern, testing the home and improving ventilation can reduce exposure.

Long-term exposure to air pollution is recognised as a cause of lung cancer. The fine particulate matter in polluted outdoor air can reach deep into the lungs and, over many years, contribute to the cell damage that leads to cancer. Indoor air pollution matters too, including smoke from burning solid cooking fuels in poorly ventilated homes. Pollution generally adds less risk than smoking, but it affects large numbers of people because it is so widespread, and the risk is greater for those who also smoke or have other exposures. Reducing exposure where you can, using cleaner cooking fuels, and improving ventilation all help lower this part of your risk.

Lung cancer is not usually inherited in a simple way, but family history does matter. Having a parent, sibling or child who has had lung cancer raises your own risk, which suggests that inherited factors play a part alongside environmental exposures. Some of this may be shared exposures within a family, such as second-hand smoke, and some may be inherited differences that make lung cells more vulnerable to damage. Separately, the cancer cells themselves often carry genetic changes that develop during a person's life rather than being inherited. Identifying these acquired changes through molecular testing can guide targeted treatment. If lung cancer runs in your family, it is worth mentioning to a specialist when discussing your risk.

Yes. Asbestos is a well-established cause of lung cancer, and the risk can appear many years after the exposure has ended. Other workplace exposures linked to lung cancer include diesel engine exhaust, silica dust, and certain industrial chemicals and metals. The danger is much greater when these exposures are combined with smoking, which multiplies the risk rather than simply adding to it. People who have worked in construction, mining, manufacturing or similar settings should mention their work history to a doctor when discussing lung health. Using protective equipment, following workplace safety measures, and not smoking all help reduce this risk.

The single most powerful step is not smoking, or quitting if you do, since the benefit begins within a few years and keeps growing. Beyond that, you can avoid second-hand smoke by keeping homes and cars smoke-free, test your home for radon if it is a concern in your area, follow safety measures around asbestos and workplace chemicals, and reduce exposure to heavy air pollution where possible. A balanced diet and regular activity support overall health but do not replace these steps. If you are in a higher-risk group, such as a current or former smoker over 50, ask a specialist whether low-dose CT screening is right for you, as catching lung cancer early makes it far more treatable. At CION, your first 45-minute consultation is free and doctor-led, with no obligation.

It is sensible to talk to a doctor if you have several risk factors, such as a long smoking history, significant exposures, or a family history of lung cancer, even if you feel completely well. You should also seek a check if you have warning signs that persist or worsen beyond three weeks, including a cough that will not go, new or worsening breathlessness, chest pain, a hoarse voice, repeated chest infections, unexplained fatigue or weight loss. Coughing up blood, even once, should be checked without waiting. Please do not panic, as many symptoms turn out to have harmless causes. A short conversation helps you understand your risk and whether a chest X-ray or low-dose CT scan is sensible. At CION, your first visit is a free 45-minute, doctor-led consultation with transparent costs and no unnecessary tests.