Smoking causes 80% to 90% of lung cancer deaths in the United States, making it the single greatest risk factor. But smoking is far from the only one. Radon gas, workplace chemicals, air pollution, family history, and certain lung diseases all raise your chances, and roughly 10% to 20% of people diagnosed with lung cancer have never smoked at all.
Smoking and Secondhand Smoke
Cigarette smoking dominates lung cancer risk more than any other factor. The longer you smoke and the more cigarettes you smoke per day, the higher your risk climbs. The measurement doctors use is “pack-years”: one pack-year equals smoking one pack per day for one year. Someone who smoked a pack a day for 20 years has a 20 pack-year history. That threshold is significant because it’s the point at which national screening guidelines kick in.
Pipes and cigars carry risk too, though cigarettes remain the most harmful. Quitting at any age reduces your risk compared to continuing, but the risk never fully returns to that of someone who never smoked. Even 15 or more years after quitting, former smokers still face elevated odds.
Secondhand smoke is responsible for roughly 7,300 lung cancer deaths per year among people who have never smoked. Living with a smoker, working in smoke-filled environments, or growing up in a household with smokers all contribute to cumulative exposure over time.
Radon Exposure at Home
Radon is the second leading cause of lung cancer overall and the leading cause among people who have never smoked. This colorless, odorless gas seeps naturally from soil and rock into buildings through cracks in foundations, gaps around pipes, and other openings. The EPA estimates radon causes about 21,000 lung cancer deaths each year in the U.S., including approximately 2,900 among never-smokers.
The EPA recommends taking action when indoor radon levels reach 4 picocuries per liter (pCi/L) or higher. Testing is inexpensive and widely available through hardware stores and local health departments. If your home tests high, mitigation systems that vent the gas from beneath your foundation typically bring levels down to safe ranges. Because radon concentrations vary house to house, even neighbors on the same street can have very different readings.
Workplace Chemical Exposure
Certain jobs expose workers to substances that directly cause lung cancer. The most well-established occupational carcinogens include asbestos (in all its forms), arsenic, beryllium, cadmium, chromium, and nickel compounds. Workers in mining, construction, shipbuilding, metalworking, and chemical manufacturing face the highest exposure levels historically, though regulations have reduced many of these risks over the decades.
Beyond those, crystalline silica dust, diesel exhaust, and chemicals produced during aluminum and coke manufacturing also increase risk. The danger compounds when occupational exposure overlaps with smoking. Asbestos workers who smoke, for example, face a dramatically higher risk than either factor alone would predict.
Air Pollution
Long-term exposure to fine particulate matter (the tiny particles called PM2.5 that come from vehicle exhaust, power plants, and industrial emissions) raises lung cancer risk even at levels common in many cities. A large meta-analysis of 17 studies found that for every 10 micrograms per cubic meter increase in PM2.5 exposure, lung cancer incidence rose by 8% and lung cancer deaths rose by 11%. That may sound modest, but for people living in heavily polluted areas over many years, the cumulative effect is meaningful. This helps explain why lung cancer rates differ between urban and rural populations and between countries with different air quality standards.
Pre-existing Lung Diseases
Chronic obstructive pulmonary disease (COPD), emphysema, and pulmonary fibrosis all independently raise the risk of developing lung cancer, even after accounting for smoking history. People with COPD face roughly 4 to 7 times the risk of lung cancer compared to those with healthy lung function, depending on the study and the severity of airflow limitation.
Even modest reductions in lung function are predictive. Research shows that a relatively small decline in how much air your lungs can push out in one second increases lung cancer risk by about 1.3 times in men and 2.6 times in women. Scarring in the lungs (fibrosis) carries a similarly elevated risk, with studies showing a roughly fivefold increase for people with fibrosis visible on CT scans. These associations hold regardless of whether the person smokes, suggesting that chronic lung inflammation itself plays a role in cancer development.
Family History and Genetics
Having a first-degree relative (parent, sibling, or child) with lung cancer raises your own risk by about 50%, according to a pooled analysis from the International Lung Cancer Consortium. This association persists after adjusting for smoking and other known risk factors, and it holds across genders, racial groups, and cancer subtypes.
In never-smokers who develop lung cancer, specific DNA mutations are often involved. The most common is a mutation in the EGFR gene, which drives tumor growth and also determines which treatments are most effective. These genetic mutations can occur spontaneously or may be inherited, though researchers are still working out the full picture of hereditary lung cancer risk.
Prior Radiation Therapy
People who received radiation to the chest for a previous cancer carry an elevated risk of developing lung cancer years later. In breast cancer survivors who had radiation, the overall relative risk was 1.8 compared to those who didn’t receive radiation, and that number climbed to 2.8 for women who were 15 or more years out from treatment. Older radiation techniques, particularly those used before the 1970s, delivered higher doses to surrounding lung tissue and carried greater risk. Modern radiation therapy is far more targeted, but any history of chest radiation remains a relevant factor.
Race, Ethnicity, and Demographics
Lung cancer rates vary significantly across racial and ethnic groups, though much of this variation traces back to differences in smoking patterns, environmental exposures, and access to healthcare. Among men, White males have the highest overall incidence at about 71 per 100,000, followed by Black males at roughly 64 per 100,000. Asian and Pacific Islander populations have the lowest rates, around 26 per 100,000 for men.
But these broad categories mask enormous internal variation. U.S.-born Black men have lung cancer rates 14% higher than White men and more than three times higher than Caribbean-born Black men. Among Hispanic populations, Cuban men have incidence rates more than double those of Central and South American men. Foreign-born Mexican women have 80% lower rates than White women. These disparities point to the powerful influence of environment, culture, and tobacco industry targeting rather than biology alone.
Who Should Get Screened
The U.S. Preventive Services Task Force recommends annual low-dose CT screening for adults aged 50 to 80 who have a 20 pack-year smoking history and either currently smoke or quit within the past 15 years. This is the only population for which routine screening is currently recommended, and catching lung cancer early through screening significantly improves survival. If you fall outside these criteria but have other risk factors (radon exposure, occupational history, family history, or prior chest radiation), it’s worth discussing your individual situation with a healthcare provider to see if screening makes sense for you.