What Causes Lung Cancer

What Really Causes Lung Cancer? A Deep Dive into the Hidden Triggers

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Medically Reviewed and Compiled by Dr. Adam N. Khan, MD.

Quick Answer: What Causes Lung Cancer?

The primary cause of lung cancer is cigarette smoking, which is responsible for approximately 80% to 90% of all cases. When you inhale tobacco smoke, you are breathing in over 7,000 chemicals, at least 70 of which are known carcinogens that damage the DNA in your lung cells. However, lung cancer also occurs in people who have never smoked. In these cases, the leading causes are radon gas exposure, long-term air pollution, secondhand smoke, and workplace toxins like asbestos.

The Anatomy of a Trigger: How Lung Cancer Starts

Lung cancer is not a single event but a process where healthy cells transform into “immortal” invaders. Normally, your body has a built-in “off switch” called apoptosis, which tells old or damaged cells to die. Cancer happens when genetic mutations—caused by external toxins or internal errors—flip that switch to “on” permanently. These cells then divide uncontrollably, forming tumors that eventually block your airways and steal oxygen from your blood.

1. The Leading Cause: Tobacco and Smoking

Smoking remains the “number one” risk factor globally. It isn’t just about the frequency of smoking, but the duration.

  • DNA Damage: The chemicals in tobacco, such as nitrosamines and polycyclic aromatic hydrocarbons, bind directly to your DNA, creating “bulky adducts” that cause permanent mutations.
  • The Multiplier Effect: If you smoke, your risk is 15 to 30 times higher than a non-smoker.
  • Other Tobacco Types: Cigars, pipes, and even “low-tar” cigarettes carry significant risks. There is no such thing as a “safe” cigarette.

2. The Silent Killer: Radon Gas

For people who have never touched a cigarette, radon gas is the most common cause of lung cancer.

  • What it is: Radon is a colorless, odorless radioactive gas that forms naturally when uranium in soil and rocks breaks down.
  • How it enters: It seeps into homes through cracks in the foundation or gaps around pipes, becoming trapped in poorly ventilated spaces like basements.
  • The Risk: Long-term exposure to high radon levels damages the lining of the lungs. Experts estimate it causes roughly 21,000 lung cancer deaths annually in the United States alone.

3. Environmental Hazards: Air Pollution and Particulates

In 2026, medical research has placed a heavier focus on outdoor air pollution as a primary driver for “never-smoker” lung cancer.

  • PM2.5 Particles: These are tiny particles (less than 2.5 microns wide) found in vehicle exhaust and industrial smoke. Because they are so small, they travel deep into the lung tissue.
  • The “Waking Up” Theory: Recent studies suggest that air pollution doesn’t just cause new mutations; it can “wake up” dormant mutant cells (like those with the EGFR mutation) that were already in the lungs, triggering them to grow into tumors.

4. Workplace and Occupational Toxins

Certain jobs expose workers to high concentrations of carcinogens. If you work in construction, mining, or manufacturing, you may face higher risks from:

  • Asbestos: Long used in insulation and roofing, breathing in asbestos fibers causes scarring and can lead to both lung cancer and mesothelioma.
  • Metals and Chemicals: Exposure to arsenic, chromium, nickel, cadmium, and diesel exhaust is strongly linked to increased cancer rates.
  • Protective Gear: Using proper safety equipment and following OSHA guidelines is essential for anyone in these industries.

5. Genetic Predisposition: Is it in Your DNA?

While lifestyle and environment cause most cases, your “nature” (genetics) also plays a role.

  • Family History: If a first-degree relative (parent or sibling) had lung cancer, your risk may be double that of the general population.
  • Specific Mutations: Non-smokers, particularly women and people of Asian descent, are more likely to have “driver mutations” like EGFR, ALK, or ROS1. These mutations allow the cancer to grow but also make it a candidate for highly effective targeted therapies.

6. Other Contributing Factors

  • Previous Lung Disease: Having conditions like COPD, emphysema, or a history of tuberculosis can cause scarring and inflammation that increases cancer risk.
  • Secondhand Smoke: Living with a smoker increases your risk of lung cancer by 20% to 30%.
  • Radiation Therapy: People who received radiation to the chest for other cancers (like breast cancer or Hodgkin lymphoma) have a slightly elevated risk later in life.

Key Takeaways for Prevention

  1. Quit Smoking: This is the single most effective way to lower your risk, regardless of your age.
  2. Test Your Home: Use a Radon Test Kit to check for invisible gas levels.
  3. Avoid Pollution: Stay indoors on days with poor air quality and advocate for cleaner air in your community.
  4. Screening: If you are over 50 and have a history of heavy smoking, talk to your doctor about a Low-Dose CT (LDCT) scan, which can find cancer early when it is most curable.

Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.