Risk factors include:
- Tobacco smoke. Smoking, of course, leads the list. Approximately 85% to 90% of people with lung cancer are present or former smokers. Passive smoking also makes you susceptible; living with a smoker can increase your risk 20% to 30%.
- Radon. Exposure to the radioactive gas emitted by uranium as it decays is the second leading cause of lung cancer deaths. Living in homes with radon levels above 4 picocuries/liter (the level deemed safe by the Environmental Protection Agency) may increase the risk for lung cancer.
- Environmental toxins. Exposure to asbestos, organic chemicals, tar, soot, or air pollution has been implicated in lung cancer development, but the relative risk posed by each of these substances hasn't been established.
- Genetics. People with a first-degree relative who developed lung cancer, especially at an early age, may be at elevated risk.