Cigarette smoking is the single biggest risk factor for lung cancer, linked to 80% to 90% of cases in the United States. But smoking isn’t the whole story. Between 20,000 and 40,000 Americans are diagnosed with lung cancer each year despite never having smoked or having smoked fewer than 100 cigarettes in their lifetime. Your age, family history, home environment, workplace exposures, and existing lung conditions all play a role in determining your overall risk.
Smokers and Former Smokers
Current smokers face the highest risk of any group. The longer you smoke and the more cigarettes you smoke per day, the greater the danger. Risk is measured in “pack-years,” a calculation that multiplies the number of packs smoked per day by the number of years you smoked. Someone who smoked one pack a day for 20 years has a 20 pack-year history, which is the threshold where annual screening becomes recommended.
Quitting does reduce your risk over time, but it doesn’t disappear. Former smokers remain at elevated risk for years after their last cigarette. The U.S. Preventive Services Task Force considers anyone who quit within the past 15 years to still be at enough risk to benefit from annual low-dose CT scans, provided they’re between 50 and 80 years old with at least a 20 pack-year history. After 15 smoke-free years, the risk drops enough that routine screening is no longer recommended.
Age and Sex
Lung cancer is overwhelmingly a disease of middle and older age. The average age at diagnosis is around 65 for both men and women. Incidence rates climb sharply starting around age 40 to 49 and peak in the 70 to 79 range for men. For women, rates tend to peak a decade earlier, in the 60 to 69 age group. Diagnoses before age 40 are uncommon.
Men develop lung cancer at higher rates than women across most age groups, though that gap has been narrowing as smoking rates among men have declined over the past several decades.
Radon Exposure at Home
Radon is a colorless, odorless gas that seeps naturally from soil and rock into buildings through cracks in foundations. It’s the second leading cause of lung cancer in the United States, responsible for roughly 21,000 deaths per year. You can’t see or smell it, so the only way to know your home’s level is to test.
The EPA recommends taking action when indoor radon reaches 4 pCi/L or higher, and considering fixes at levels between 2 and 4 pCi/L. To put the numbers in perspective: out of every 1,000 people exposed to 4 pCi/L over a lifetime, about 62 could develop lung cancer. At 10 pCi/L, that number jumps to roughly 150. Testing kits are inexpensive and widely available at hardware stores, and mitigation systems can typically bring levels down significantly.
Secondhand Smoke
Living with a smoker meaningfully raises your lung cancer risk even if you never light a cigarette yourself. A large meta-analysis covering 82 studies found that never-smokers exposed to secondhand smoke have a 24% higher risk of developing lung cancer compared to those who aren’t exposed. The risk from household exposure specifically was about 20% higher. Years of daily exposure in a shared home or car add up in ways that occasional encounters in public spaces do not.
Workplace Carcinogens
Certain jobs carry built-in lung cancer risk because of the materials workers breathe. Asbestos is the most well-known, but arsenic, diesel exhaust, silica dust, and certain forms of chromium are also established carcinogens. Industries like construction, mining, manufacturing, and trucking can involve prolonged contact with these substances.
The risk is compounded for workers who also smoke. Asbestos exposure alone raises lung cancer risk, but asbestos exposure combined with smoking multiplies it far beyond what either factor would cause on its own. If you’ve worked in a high-exposure trade, that history is worth mentioning to your doctor even decades later.
Family History
Genetics play a role that’s independent of smoking. A pooled analysis from the International Lung Cancer Consortium found that having a first-degree relative (parent, sibling, or child) with lung cancer raises your own risk by about 50%, even after adjusting for smoking status and other known risk factors. This increased risk holds regardless of gender, race, or the specific type of lung cancer involved.
Researchers haven’t pinpointed a single “lung cancer gene” in the way BRCA mutations are linked to breast cancer, but the familial pattern is consistent enough that a strong family history should factor into conversations about screening, particularly if you have other risk factors stacked alongside it.
Pre-Existing Lung Disease
Chronic lung conditions create an environment where cancer is more likely to develop. COPD (chronic obstructive pulmonary disease) is associated with a lung cancer incidence of roughly 7% to 11%. Idiopathic pulmonary fibrosis, a condition where lung tissue becomes scarred and stiff, carries an even higher incidence of about 22% to 31%.
The most dangerous combination is having both emphysema and pulmonary fibrosis together, a condition called combined pulmonary fibrosis and emphysema. Studies have found lung cancer rates of 36% to 47% in this group, likely because of a “triple hit” effect from smoking damage, airway destruction, and scar tissue all promoting abnormal cell growth simultaneously.
Racial Disparities
Lung cancer does not affect all racial groups equally in the United States. Black Americans have historically had the highest mortality rates, while Asian and Pacific Islander Americans have had the lowest. When researchers tracked five-year outcomes for lung cancer patients diagnosed between 2000 and 2019, Black patients had the highest cumulative death rate at 84.9%, compared to 81.8% for White patients and 77.4% for Asian and Pacific Islander patients.
These gaps reflect a mix of factors: differences in smoking prevalence, unequal access to early screening and treatment, environmental exposures that vary by neighborhood, and possible biological differences in how tumors behave. The good news is the disparity has been narrowing. The mortality gap between Black and White patients shrank measurably over the two decades studied, though it hasn’t closed entirely.
Lung Cancer in Never-Smokers
Lung cancer in people who have never smoked behaves differently at the molecular level. Tumors in never-smokers are far more likely to be driven by specific genetic mutations that can be targeted with newer therapies. About 36% of lung cancers in non-smokers carry mutations in a growth-signaling pathway called EGFR, compared to just 8% in smokers. Similarly, a rearrangement in another gene called ALK shows up in about 26% of non-smoker lung cancers versus 4% in smokers.
This matters practically because these mutations often respond well to targeted drugs, which tend to have fewer side effects than traditional chemotherapy. If you’re a non-smoker diagnosed with lung cancer, molecular testing of your tumor is a critical step that can open the door to more effective, better-tolerated treatments.
Who Should Be Screened
The current recommendation from the U.S. Preventive Services Task Force is 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 was expanded in recent years from the previous criteria, which started at age 55 and required 30 pack-years, meaning more people now qualify.
A pack-year is straightforward to calculate: one pack per day for one year equals one pack-year. Two packs a day for 10 years also equals 20 pack-years. If you’re unsure whether you qualify, add up your history and bring it to your next appointment. Early detection through screening catches lung cancer at stages where survival rates are dramatically better.