Lung cancer has always been thought of as a smoker’s disease. That is still largely true, but the story is changing in an important way. A growing share of lung cancer is now being diagnosed in people who have never smoked. Globally, about 15-20% of lung cancer cases occur in never-smokers. That means if lung cancer in never-smokers were its own disease category, it would still rank as the fifth leading cause of cancer death worldwide.

Two things are happening at the same time. First, smoking rates are falling in many countries. That is excellent news. But as smoking-related lung cancer declines, cancers driven by other factors become a larger slice of the pie. Second, the actual incidence rate of certain lung cancers appears to be rising in never-smokers in some regions. When you combine that with population growth and aging, the absolute number of cases in never-smokers is likely increasing, not just the percentage.

I researched and wrote today’s post (#66) because of a conversation with my friend Vivek who mentioned that one of his acquaintances was diagnosed with stage 4 lung cancer, in his early 50s, in spite of never having been a smoker.

What is driving lung cancer in people who have never touched a cigarette?

Air pollution is a big one. Fine particulate matter (PM2.5) from traffic, industry, and fossil fuels is classified as a known human carcinogen. Newer research suggests that air pollution doesn’t just damage DNA directly like tobacco smoke does; instead, it can act as a “trigger.” We all have rare, dormant mutations in our lung cells as we age. Most never cause any problems. However, pollution can cause inflammation that “wakes up” these dormant cells, causing them to grow uncontrollably.

Indoor air can matter just as much. Radon is a naturally occurring radioactive gas released in small amounts from rocks and soil. Outdoors, it gets dispersed causing no harm, but it can seep from the ground into homes especially basements or enclosed spaces, and is the leading cause of lung cancer in never-smokers. In the U.S. alone, it is responsible for roughly 21,000 lung cancer deaths annually. Secondhand smoke also remains a serious factor, increasing a non-smoker’s risk by 20 to 30 percent. In some regions, cooking with solid fuels or heavy exposure to cooking fumes can also play a role. Add in occupational exposures like asbestos or diesel exhaust, and you start to see a pattern. This is not one single cause. It is a mix of environmental hits over decades.

A different biology

Biology also differs significantly. Lung cancers in never-smokers often have different genetic “drivers” than smoking-related cancers.

These cancers are more common in women and in certain Asian populations. E.g., among East Asian women who have never smoked, certain mutations (EGFR) can be found in over 50 percent of cases. This tells us we are dealing with a distinct disease process, not just a milder version of smoking-related lung cancer. The silver lining is that these specific mutations often respond exceptionally well to newer targeted therapies, which are oral pills that can control the cancer with far fewer side effects than traditional chemotherapy.

The challenge of early detection

The hard part is early detection. Symptoms such as cough, breathlessness, or chest pain usually show up late. And because doctors and patients often associate lung cancer with smoking, diagnosis in never-smokers can be delayed by weeks or months, as symptoms are often mistaken for lingering colds or asthma.

Right now, the only screening test proven to reduce lung cancer deaths is a low-dose CT (LDCT) scan of the chest. Large trials showed it saves lives in heavy smokers. Because their risk is significantly higher, screening makes sense in this group. That is why current guidelines focus on people aged 50 to 80 with a 20 pack-year (i.e. 1 pack per day for 20 years) smoking history.

For never-smokers, routine screening is not currently recommended because the overall risk per person is lower, and the risk of “false positives” (finding spots that aren’t cancer) can lead to unnecessary, invasive procedures. However, the medical community is beginning to explore risk-based screening that looks at family history, radon exposure, and air quality to identify high-risk non-smokers who might benefit from a scan.

Actionable steps: What you can do today

So what can a never-smoker actually do today that is practical?

Test your home for radon. If you live in a region known for higher natural radon levels, then this is the most important actionable step. Testing kits are cheap and simple to use. If levels are high (above 4 pCi/L), mitigation systems can reduce radon levels by up to 99 percent. I haven’t done this as yet but now plan to. Newly added: Dr. Ali Zaidi pointed me to a website that shows radon levels by zip code. https://share.google/pm4WlDPCC8z3XOaPy. I happen to luckily be living in an area with an average level of 2 pCi/L).

Pay attention to air quality. Use HEPA air purifiers indoors if you live in polluted areas or near highways. Avoid exercising outdoors right next to heavy traffic during rush hour. On “Code Red” air quality days, reduce outdoor exposure. Note, as per the image, the definitions of satisfactory and unhealthy levels differ across countries so just because the weather service deems something satisfactory, doesn’t make it so. We have been using air purifiers inside the house for a while.

Take occupational exposures seriously. If you work around dust, fumes, or industrial chemicals, protective equipment and proper ventilation are not optional. I don’t have to deal with this issue, fortunately.

Do not ignore persistent symptoms. A cough that does not go away (lasting more than 3 weeks), unexplained weight loss, coughing up blood, or new shortness of breath deserves medical evaluation, regardless of your smoking history. I will definitely be keeping a look out for this without becoming paranoid.

The bottom line

The big mindset shift is this: Lung cancer is not only a smoker’s disease anymore. Smoking is still the dominant risk, but environmental and biological factors mean that never-smokers are not immune. The goal is not to create fear. It is to focus on the high-leverage steps we can control, especially radon and air quality, while staying alert to symptoms and having informed discussions with your doctor if you have other risk factors like a strong family history.

As always, I welcome your thoughts and would love to hear your experiences in the comments.

Nickhil Jakatdar is the CEO of GenePath Diagnostics and the founder of PreventiveHealth.ai, working to make advanced diagnostics and credible health guidance more accessible, affordable, and actionable. A PhD in EECS from UC Berkeley and the youngest recipient of the UC Berkeley Distinguished Alumnus Award, he has founded and led multiple tech companies. He holds 60 patents, and serves on several academic, healthcare, and innovation boards. To follow his thinking on preventive health, technology, and systems that scale expertise, join his private WhatsApp community and subscribe to his Substack.

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