Lung Cancer Causes and Risk Factors

Key Takeaways

• Smoking is the leading cause of lung cancer, accounting for 80–85% of cases, but quitting significantly reduces risk over time and improves outcomes for those already diagnosed.

• Radon is the second leading preventable cause of lung cancer; testing your home is simple and inexpensive, and mitigation can effectively reduce exposure.

• Occupational and environmental exposures—including asbestos, diesel exhaust, air pollution, and chemical compounds—increase lung cancer risk, particularly when combined with smoking.

• Genetics and family history contribute to lung cancer risk, and certain inherited mutations may increase susceptibility regardless of other exposures.

• Lung cancer in non-smokers is becoming increasingly common, particularly among women and younger adults, and should never be accompanied by shame or stigma. All lung cancer patients deserve compassionate care.

• Understanding your specific risk factors and cancer characteristics—including biomarker status—helps your medical team personalize your treatment plan and identify potential clinical trials that may be appropriate for you.

Introduction

Lung cancer is one of the most commonly diagnosed cancers worldwide, affecting hundreds of thousands of people each year. If you or a loved one has received a lung cancer diagnosis, understanding what may have caused it is a natural first step. However, it's important to know that lung cancer develops from a combination of factors and in many cases, there is no single "cause" that can be pinpointed. According to the American Cancer Society and National Cancer Institute, multiple risk factors can accumulate over time to increase the likelihood of developing lung cancer.

The good news is that understanding these risk factors empowers you. By learning what increases the risk of lung cancer, you can take steps to reduce your own risk, make informed conversations with your healthcare providers, and better understand how your specific circumstances may influence your treatment options and prognosis.

It's equally important to acknowledge that many people who develop lung cancer feel a sense of shame or self-blame, particularly those with smoking histories or no obvious risk factors. This stigma is unwarranted. Lung cancer is a disease, not a moral failing, and people deserve compassionate, judgment-free medical care regardless of how they may have developed the condition.

Smoking and Lung Cancer

The Leading Cause of Lung Cancer

Cigarette smoking remains the single largest preventable cause of lung cancer. According to the CDC, smoking accounts for approximately 80–85% of all lung cancer cases. This statistic reflects not only the widespread use of cigarettes but also their potent carcinogenic properties.

How Smoking Damages Lung Tissue

When smoke is inhaled, it exposes lung cells to hundreds of toxic and cancer-causing chemicals, including benzopyrene, nitrosamines, and polonium-210. Repeated exposure to these carcinogens damages the DNA in lung cells, leading to mutations that can eventually result in malignant transformation. The risk is directly related to the dose and duration of exposure, a relationship known as the "dose-response relationship." People who smoke more cigarettes per day or smoke for longer periods face higher risk.

Cigarettes, Cigars, and Pipes

While cigarettes carry the highest documented risk, other forms of smoking also increase lung cancer risk. Cigars often contain more tobacco than a single cigarette and may expose users to even higher concentrations of carcinogens. Pipe smoking similarly increases lung cancer risk, though the absolute risk may be slightly lower than cigarette smoking. The key takeaway is there is no truly "safe" level of tobacco smoke inhalation.

Secondhand Smoke Exposure

Secondhand smoke (also called environmental tobacco smoke or passive smoke) is classified as a human carcinogen by the International Agency for Research on Cancer (IARC). Non-smokers exposed to secondhand smoke at home or in the workplace have a 20–30% increased risk of developing lung cancer compared to those with no secondhand smoke exposure. This risk applies regardless of whether the exposed person has ever smoked themselves. Importantly, children and adolescents exposed to secondhand smoke in their homes face increased lung cancer risk in adulthood.

The Path to Recovery: Smoking Cessation

One of the most empowering pieces of evidence is that quitting smoking significantly reduces lung cancer risk. According to the American Cancer Society, people who quit smoking can reduce their lung cancer risk by up to 50% over 10 years compared to continuing smokers. Even for those who have already developed lung cancer, quitting improves overall health, enhances immune function, and may improve treatment outcomes and quality of life.

Radon Exposure

The Second Leading Cause

Radon is the second leading preventable cause of lung cancer after smoking, accounting for an estimated 21,000 lung cancer deaths annually in the United States, according to the EPA and CDC. Yet radon remains less well-known to the general public than smoking, likely because it is invisible, odorless, and colorless.

What Is Radon?

Radon is a naturally occurring, radioactive gas that forms from the decay of uranium and radium in soil and rock. It is present to some degree everywhere, but concentrations vary dramatically by geography and geology. When radon gas is inhaled, radioactive particles can lodge in the lungs, where they continue to decay and emit radiation that damages lung tissue cells.

How Radon Enters Homes

Radon typically enters buildings through cracks and gaps in foundations, around pipes, sump pumps, and crawl spaces. Because radon is heavier than air, it tends to accumulate in basements and lower levels. Homes with poor ventilation or those built in areas with naturally high radon in the surrounding geology face the highest risk. Radon can also accumulate in underground spaces, though some buildings are at minimal risk.

EPA Guidelines and Safe Levels

The EPA recommends that homes maintain radon levels below 2.0 picocuries per liter (pCi/L). Levels above this threshold are considered elevated and warrant remediation efforts. The EPA provides detailed information on radon testing and mitigation strategies on its website.

Testing Is Simple and Inexpensive

One of the most positive aspects of radon is that testing is straightforward and affordable. Short-term tests can be completed in 2–7 days, while long-term tests provide more comprehensive data over 3–12 months. Many states offer free or low-cost radon testing kits. If elevated radon is detected, remediation measures, such as improving ventilation, sealing foundation cracks, or installing sub-slab depressurization systems, can effectively reduce radon levels in the home.

Occupational and Environmental Exposures

Workplace Carcinogens

Beyond radon and secondhand smoke, numerous occupational and environmental exposures increase lung cancer risk. These include asbestos, diesel exhaust, air pollution, and specific chemical compounds.

Asbestos

Asbestos is a fibrous mineral that was widely used in insulation, roofing materials, brake pads, and other industrial applications throughout much of the 20th century. When asbestos fibers are inhaled, they can lodge in the lungs and cause scarring and inflammation. Long-term asbestos exposure significantly increases the risk of lung cancer, and the effect is synergistic with smoking, meaning smokers exposed to asbestos face a dramatically elevated risk. Although many asbestos-containing products are now banned or heavily regulated in developed countries, older buildings and certain occupations still pose exposure risks.

Diesel Exhaust and Other Chemical Exposures

Truck drivers, railroad workers, and miners, may be exposed to high amounts of diesel exhaust,  a recognized carcinogen. Long-term exposure to diesel exhaust increases lung cancer risk. Similarly, workers in certain industries may be exposed to chromium, arsenic, nickel, or beryllium—all of which are linked to elevated lung cancer risk. Coal miners and workers in iron foundries also face increased risk from their occupational exposures.

Air Pollution

Outdoor air pollution, particularly fine particulate matter (PM 2.5) and ozone, is associated with increased lung cancer risk. According to the IARC, outdoor air pollution is classified as a Group 1 carcinogen. People living in areas with high levels of air pollution face elevated lung cancer risk, and this risk appears to be independent of smoking status. As urbanization and industrial activity continue worldwide, air pollution remains a significant public health concern.

Workplace Safety and Regulation

For individuals who work in industries with known occupational exposures, adhering to workplace safety protocols is essential. This includes using proper respiratory protection, ensuring adequate ventilation, and following regulations set by the Occupational Safety and Health Administration (OSHA) and similar bodies. Regular health screenings for high-risk occupational groups can enable early detection and intervention.

Genetics and Family History

Inherited Susceptibility

While most lung cancers result from environmental or behavioral risk factors, genetics plays an important role. Some families have inherited susceptibility to lung cancer, meaning that family members face elevated risk even with lower exposure to traditional risk factors. This hereditary predisposition may be due to variations in genes involved in DNA repair, detoxification of carcinogens, or cell cycle control.

The Impact of Family History

Having a first-degree relative (parent, sibling, or child) with lung cancer increases your own risk of developing the disease. This increased risk is observed even among non-smokers, suggesting that inherited factors contribute significantly. The risk is highest when multiple family members have developed lung cancer, particularly if they were diagnosed at younger ages (before 65).

Genetic Mutations and Lung Cancer

Certain inherited genetic mutations increase lung cancer susceptibility. For example, mutations in the TP53 gene (the "guardian of the genome") increase risk across multiple cancer types, including lung cancer. Additionally, variations in genes involved in metabolizing carcinogens—such as the cytochrome P450 family—may influence individual susceptibility to lung cancer from smoking or other exposures.

Non-Smoker Lung Cancers and Genetic Factors

Lung cancers that develop in people with no smoking history are often associated with specific genetic mutations, such as mutations in the EGFR, ALK, KRAS, or ROS1 genes. Understanding these mutations has profound clinical implications, as many can be targeted with specific medications (see the section on treatment below).

Lung Cancer in Non-Smokers

A Growing Population

Approximately 10–20% of all lung cancer cases occur in people who have never smoked. In some countries, this proportion is even higher—approaching 30–40% in Asia. Importantly, lung cancer in never-smokers is an increasingly recognized clinical entity, and it is becoming more common, particularly among women and younger adults.

Why Non-Smokers Develop Lung Cancer

Never-smokers who develop lung cancer typically have exposure to other risk factors. The most common causes include radon exposure, secondhand smoke, occupational exposures, air pollution, and genetic predisposition. In many cases, a combination of factors contributes to disease development.

The Rise of Lung Cancer in Non-Smoking Women

One notable epidemiological trend is the increase in lung cancer diagnoses among women who have never smoked. Several hypotheses explain this pattern, including increased occupational exposures, greater use of cooking oils and fumes, exposure to secondhand smoke from spouses or family members, and increased screening and detection. Genetics and hormone-related factors may also play roles.

Destigmatization and Compassionate Care

A critical message for people who develop lung cancer without a smoking history is that they should not feel uniquely blamed or stigmatized. All lung cancer patients deserve evidence-based, compassionate medical care. The lung cancer community has worked hard to reduce stigma and ensure that people understand that lung cancer is not a "smoker's disease"—it affects people across all demographics and risk profiles.

Reducing Your Risk

Smoking Cessation

If you currently smoke, the single most impactful step you can take to reduce your lung cancer risk is to quit. Numerous evidence-based resources and treatments are available, including nicotine replacement therapy, prescription medications (such as varenicline and bupropion), behavioral counseling, and smoking cessation programs. Your healthcare provider can help you develop a personalized quit plan.

Radon Testing and Mitigation

Test your home for radon, particularly if you live in an area with naturally elevated radon. Contact your state radon program or visit the EPA website for information on testing kits and certified professionals. If radon levels are elevated, invest in remediation to reduce risk for you and your family.

Occupational Safety

If your work exposes you to known carcinogens, follow all workplace safety protocols rigorously. Wear appropriate respiratory protection, ensure adequate ventilation, and participate in regular health screenings if offered. Know your rights under occupational safety regulations and report hazardous conditions to appropriate authorities.

Lung Cancer Screening

High-risk individuals—particularly those with significant smoking histories—may be candidates for low-dose CT screening, which can detect lung cancer at earlier, more treatable stages. If you meet screening criteria, discuss this with your healthcare provider.

Healthy Lifestyle Choices

While not a guarantee against lung cancer, maintaining overall health through regular physical activity, a diet rich in fruits and vegetables, limiting alcohol, and managing stress supports your general wellness and may reduce risk of multiple health conditions.

How Understanding Causes Connects to Treatment

Cause and Cancer Type

The underlying cause of lung cancer often correlates with the type of cancer that develops. For example, smoking is associated with squamous cell carcinoma and small cell lung cancer, while adenocarcinoma—which arises in mucus-secreting cells—is more common in non-smokers. Understanding your cancer type helps your oncologist recommend appropriate treatment strategies.

Biomarker Testing and Targeted Therapy

In recent years, the field of lung cancer treatment has been revolutionized by the discovery of specific genetic mutations and biomarkers in cancer cells. Non-smoker lung cancers, in particular, are frequently found to carry actionable mutations such as EGFR, ALK, ROS1, or KRAS mutations. These mutations can be targeted with targeted therapy medications, which attack cancer cells with greater precision and often cause fewer side effects than traditional chemotherapy.

Your medical team will recommend biomarker testing on your tumor tissue or blood to identify any mutations present. If a mutation is found, a targeted therapy designed to inhibit that specific mutation may be recommended as your primary treatment.

Immunotherapy and Other Treatment Options

For tumors without actionable mutations, immunotherapy has emerged as a powerful treatment option. These drugs harness your immune system to recognize and attack cancer cells. Additionally, traditional chemotherapy remains an important tool, often combined with other modalities.

Connecting Cause to Prognosis

While the cause of lung cancer doesn't solely determine prognosis, understanding your specific circumstances—including the cause, cancer stage, histology, and biomarker status—helps your team develop a personalized treatment plan. Recent advances mean that even advanced lung cancers can often be effectively managed, particularly when tailored to the individual's specific cancer characteristics.

Exploring Clinical Trials

Clinical trials are research studies testing new treatments or novel combinations of existing treatments. If you have advanced lung cancer or have exhausted standard treatment options, a clinical trial may provide access to cutting-edge therapies. Participating in a trial contributes to advancing lung cancer treatment for future patients while potentially providing you access to new options.

Ready to explore clinical trials that may be right for you? Start your search with North's trial finder.

Frequently Asked Questions

Can non-smokers get lung cancer?

Yes, absolutely. Approximately 10–20% of lung cancer cases occur in people who have never smoked. Non-smokers can develop lung cancer from radon exposure, secondhand smoke, occupational hazards, air pollution, and genetic factors. Lung cancer in non-smokers is an important and increasingly common diagnosis, and it should never be accompanied by shame or self-blame.

How much secondhand smoke exposure increases lung cancer risk?

Non-smokers exposed to secondhand smoke at home or in the workplace have a 20–30% increased risk of developing lung cancer compared to those with no exposure. Even brief or intermittent exposure over many years can accumulate to increase risk. Children and adolescents exposed to secondhand smoke in their homes face increased lung cancer risk in adulthood.

What is the relationship between radon and lung cancer?

Radon is a naturally occurring radioactive gas that enters homes through foundation cracks and gaps. When inhaled, radon particles lodge in the lungs and emit radiation that damages lung tissue cells. The EPA estimates that radon causes approximately 21,000 lung cancer deaths annually in the United States. Testing is simple and inexpensive, and mitigation measures can effectively reduce radon levels.

Does quitting smoking reduce lung cancer risk?

Yes, significantly. Quitting smoking reduces lung cancer risk by approximately 50% over 10 years compared to continuing smokers. Even for those already diagnosed with lung cancer, quitting improves overall health, immune function, and treatment outcomes. It's never too late to quit.

How do genetics influence lung cancer risk?

Some families have inherited susceptibility to lung cancer due to variations in genes involved in DNA repair, carcinogen detoxification, and cell cycle control. Having a first-degree relative with lung cancer increases your own risk, particularly if the relative was diagnosed at a younger age. Additionally, certain inherited mutations—such as TP53 mutations—increase cancer risk across multiple types, including lung cancer.

What role do genetic mutations play in treatment?

Genetic mutations in cancer cells—such as EGFR, ALK, ROS1, or KRAS mutations—can be targeted with targeted therapy medications that attack cancer cells with greater precision. Biomarker testing on your tumor tissue or blood identifies any actionable mutations, allowing your oncologist to recommend the most effective personalized treatment strategy.

References

1. American Cancer Society. "Lung Cancer Key Statistics." cancer.org.

2. Centers for Disease Control and Prevention. "What Are the Risk Factors for Lung Cancer?" cdc.gov.

3. International Agency for Research on Cancer. "IARC Monographs on the Identification of Carcinogenic Hazards to Humans." iarc.who.int.

4. National Cancer Institute. "Lung Cancer Prevention (PDQ) — Patient Version." cancer.gov.

5. U.S. Environmental Protection Agency. "Radon." epa.gov.

6. Occupational Safety and Health Administration. "Asbestos." osha.gov.

7. American Thoracic Society. "Lung Cancer Patient Resources." thoracic.org.